I am a Professor of Economics and Associate Dean in the Social Science Division of New York University Abu Dhabi as well as an affiliated researcher in the Luxembourg Institute of Socio-Economic Research (LISER). My main research interests lie within behavioral economics and public policy. In particular, I focus on the emergence and enforcement of prosocial norms, the behavioral determinants of labor market outcomes, and the effect of biases on discrimination. I regularly organize the international Symposium in Experimental Economics (iSEE). Finally, I am one of the founding researchers of the Center for Behavioral Institutional Design.
Recent research has found that competitive behavior measured in experiments strongly predicts individual differences in educational and labor market outcomes. However, there is no consensus on the underlying factors behind competitive behavior in these experiments. Are participants who compete more capable, more confident, and more tolerant of risk, or are they competing because they enjoy competition per se? In this study, we present an experiment designed to measure individuals' preferences for competition. Compared to previous work, our experiment rules out risk preferences by design, measures beliefs more precisely, and allows us to measure the magnitude of preferences for competition. In addition, we collect multiple decisions per participant, which lets us evaluate the impact of noisy decision-making. We find strong evidence that many individuals possess preferences for competition. Most participants are either reliably competition-seeking or competition-averse, and their choices are highly consistent with expected utility maximization. We also find that preferences for competition depend on the number of competitors but not on the participants' gender.
This paper investigates gender differences in the job search process, both in the field and lab. First, we collect rich information on job offers and acceptances from undergraduates of Boston University’s Questrom School of Business. We document two novel empirical facts: (1) there is a clear gender difference in the timing of job offer acceptance, with women accepting jobs substantially earlier than men, and (2) the gender earnings gap in accepted offers narrows in favor of women over the course of the job search period. To rationalize these patterns, we develop a job search model that incorporates gender differences in risk aversion and overoptimism about prospective offers. We validate the model assumptions and predictions using the survey data, and present empirical evidence that the job search patterns in the field can be partly explained by greater risk aversion displayed by women and the higher levels of overoptimism (and slower belief updating) displayed by men. Next, we replicate the findings from the field in a specially-designed laboratory experiment that features sequential job search, and provide direct evidence on the purported mechanisms. Our findings highlight the importance of risk preferences and beliefs for gender differences in job-finding behavior, and consequently, early career wage gaps among the highly-skilled.
We study whether and why taste for competition (as measured by Niederle and Vesterlund, 2007) affects MBA salaries and whether this effect can explain the wage gender gap. At graduation, MBAs with higher taste for competition earn $15K (9.3%) more. Over time this effect is mitigated by overconfidence. Seven years after graduation, competitive MBAs with a low degree of overconfidence earn 26% more, while those who are highly overconfident earn 19% less. Taste for competition explains 10% of the gender gap at graduation and none seven years later.
In this paper, we study the effects of business culture on market efficiency. We exogenously vary the type of business culture between business-is-business cultures, which consist on impersonal relationships where financial matters are paramount, and business-is-family cultures, which comprise of cohesive personal relationships where financial matters and personal attachments are intertwined. We use a laboratory experiment to assess the effect of business cultures in environments with different degrees of contract enforceability and competition. Our main results indicate that business-is-family cultures are more effective when contracts are unverifiable because they help market participants overcome problems of trust. On the other hand, we find that business-is-business cultures are more effective in competitive settings because they facilitate the severance of ties with unproductive partners.
We study the role of fairness principles as focal points in coordination problems with homogeneous and heterogeneous agents. To this end we elicit normatively fair ways of how the coordination game should be played. We find that in homogeneous groups people implicitly agree on a unique fair way of playing the game while in heterogeneous groups well-defined multiple but conflicting fairness principles prevail. In the subsequent repeated coordination game homogeneous groups most of the time successfully coordinate on the equilibrium consistent with the unique fairness principle of equality. In heterogeneous groups coordination often fails or is inefficient. Interestingly, heterogeneous groups are equally likely as homogeneous groups in achieving coordination but are less likely to stay coordinated. In both types of groups only equilibria consistent with a fairness principle are stable. Individual level analysis reveals that individual fairness principles and expectations about others' fairness principles are, on the one hand, important for staying coordinated but, on the other hand, also responsible for leaving even efficient coordination equilibria that are not in concordance with one of the fairness principles. Hence, fairness principles can lead to success but may also induce failure in coordination problems.
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Despite increased female educational attainment and labor market participation, labor markets around the world remain characterized by vertical and horizontal gender segregation. This chapter reviews recent findings from the experimental economics literature that shed light on some of the causes of gender differences in labor market outcomes. First, it reviews the recent literature using incentivized measures of attitudes toward risk and competition to study the extent to which gender differences in these traits help explain gender differences in educational and career choices as well as earnings. Second, it reviews the experimental literature on gender differences in negotiations. Third, it concludes by discussing the recent experimental literature on gender discrimination, emphasizing beliefs about productivity as the mechanism leading to differential hiring of men and women. Experiments are a powerful tool to explain gender differences in labor markets as they create controlled environments where causal links can be derived and exact mechanisms can be identified.
We report data on the experimental articles published from 2000 to 2021 in seven leading general-interest economics journals. We also look at time trends in the characteristics of the published experimental articles, including citations and the nationality of the authors. We find an overall increasing trend in the publication of non-lab experiments in all journals. By contrast, the share of lab experiments has more than halved in the AER and remained low in other Top five journals. The diverging trends for non-lab and lab experiments are not universal as the shares of both have increased in two other high-ranking economics journals (JEEA and EJ). We also observe some heterogeneities in publication, citations, rankings, and locations of authors' affiliations across journals and types of experiments.
We investigate the effects of group identity on hiring decisions with adverse selection problems. We run a laboratory experiment in which employers cannot observe a worker's ability nor verify the veracity of the ability the worker claims to have. We evaluate whether sharing an identity results in employers discriminating in favor of ingroup workers, and whether it helps workers and employers overcome the adverse selection problem. We induce identities using the minimal group paradigm and study two settings: one where workers cannot change their identity and one where they can. Although sharing a common identity does not make the worker's claims more honest, employers strongly discriminate in favor of ingroup workers when identities are fixed. Discrimination cannot be explained by employers' beliefs and hence seems to be taste-based. When possible, few workers change their identity. However, the mere possibility of changing identities erodes the employers' trust towards ingroup workers and eliminates discrimination.
A growing body of research shows that people tend to act more antisocially in groups than alone. However, little is known about why having "partners in crime" has such an effect. We run an experiment using sender-receiver games in which we elicit subjects' normative and empirical beliefs to shed light on potential driving factors of this phenomenon. We find that the involvement of an additional sender makes the antisocial actions of senders more normatively acceptable to all parties, including receivers. By contrast, empirical beliefs are unaffected by the additional sender, suggesting that antisocial behavior increases in groups because antisocial actions become more acceptable and not because acceptable behavior is expected less often. We identify a necessary condition for this effect: the additional sender has to actively participate in the decision-making
This study investigates whether asking early adolescents to evaluate the food choices of remote peers improves their own food selection. Participants were students from fifth (N = 219, Mage = 9.30 years) and sixth grades (N = 248, Mage = 10.28 years) of varying nationalities living in the United Arab Emirates (race and ethnicity were not collected). Students saw peers' healthy or unhealthy food choices before picking their own food. In some conditions, students also critically evaluated the healthiness of the peers' choices. Evaluation of peer choices led to healthier decisions (d = 0.53) to the point that it offsets the negative impact of observing unhealthy peer choices. This effect is larger for sixth graders compared to fifth graders.
We run an experimental study using sender-receiver games to evaluate how senders' willingness to lie to others compares to their willingness to tell hard truths, i.e., promote an outcome that the sender know is unfair to the receiver without explicitly lying. Unlike in previous work on lying when it has consequences, we do not find that antisocial behavior is less frequent when it involves lying than when it does not. In fact, we find the opposite result in the setting where there is social contact between senders and receivers, and receivers have enough information to judge whether they have been treated unfairly. In this setting, we find that senders prefer to hide behind a lie and implement the antisocial outcome by being dishonest rather than by telling the truth. These results are consistent with social image costs depending on the social proximity between senders and receivers, especially when receivers can judge the kindness of the senders' actions.
We study whether gender influences credit attribution for group work using observational data and two experiments. We use data from academic economists to test whether coauthorship matters differently for tenure for men and women. We find that conditional on quality and other observables, men are tenured similarly regardless of whether they coauthor or solo-author. Women, however, are less likely to receive tenure the more they coauthor. We then conduct two experiments that demonstrate that biases in credit attribution in settings without confounds exist. Taken together, our results are best explained by gender and stereotypes influencing credit attribution for group work.
We validate experimentally a new survey item to measure the preference for competition. The item, which measures participants' agreement with the statement "Competition brings the best out of me", predicts individuals' willingness to compete in the laboratory after controlling for their ability, beliefs, and risk attitude (Niederle and Verterlund, 2007). We further validate the explanatory power of our survey item outside of the laboratory, by comparing responses across two samples with predicted differences in their preference for competition: professional athletes and non-athletes. As predicted, we find that athletes score higher on the item than non-athletes.
One of the foundations of economic theory is that the choices individuals make are driven by their preferences. Importantly for economic modeling, preferences are commonly assumed to be rationalizable by a utility function. The predictive ability of most microeconomic models relies on properly quantifying these preferences and their rationalizability. Hence, this is a challenging but necessary task. In this chapter, we discuss methodologies used in experimental economics to measure preference and their degree of consistency with utility maximization. Topics include the measurement of risk, intertemporal, and social preferences. Moreover, we discuss the effects of manipulating revealed preferences though framing and the revelation of normative information.
We study the effect on coordination in a minimum-effort game of a leader's gender depending on whether the leader is democratically elected or is randomly-selected. Leaders use non-binding messages to try to convince followers to coordinate on the Pareto-efficient equilibrium. We find that teams with elected leaders coordinate on higher effort levels. Initially, the benefits of being elected are captured solely by male leaders. However, this gender difference disappears with repeated interaction because unsuccessful male leaders are reelected more often than unsuccessful female leaders.
We study the strategies used by experimental subjects in repeated sequential prisoners' dilemma games to identify the underlying motivations behind instrumental reciprocity, that is, reciprocation of cooperation only if there is future interaction. Importantly, we designed the games so that instrumental reciprocity is a mistake for payoff-maximizing individuals irrespective of their beliefs. We find that, despite the fact that instrumental reciprocity is suboptimal, it is one of the most frequently used cooperative strategies. Moreover, although the use of instrumental reciprocity is sensitive to the costs of deviating from the payoff-maximizing strategy, these costs alone cannot explain the high frequency with which subjects choose to reciprocate instrumentally.
In this paper, we study two games of conflict characterized by unequal access to productive resources and finitely repeated interaction. In the Noisy Conflict game, the winner of the conflict is randomly determined depending on a players' relative conflict expenditures. In the Decisive Conflict game, the winner of the conflict is simply the player who spends more on conflict. By comparing behavior in the two games, we evaluate the effect that "decisiveness" has on the allocation of productive resources to conflict, the resulting inequality in the players' final wealth, and the likelihood that players from long-lasting peaceful relations.
Standard observed characteristics explain only part of the differences between men and women in education choices and labor market trajectories. Using an experiment to derive students' levels of overconfidence, and preferences for competitiveness and risk, this paper investigates whether these behavioral biases and preferences explain gender differences in college major choices and expected future earnings. In a sample of high-ability undergraduates, we find that competitiveness and overconfidence, but not risk aversion, is systematically related with expectations about future earnings: individuals who are overconfident and overly competitive have significantly higher earnings expectations. Moreover, gender differences in overconfidence and competitiveness explain about 18\% of the gender gap in earnings expectations. These experimental measures explain as much of the gender gap in earnings expectations as a rich set of control variables, including test scores and family background, and they are poorly proxied by these same control variables, underscoring that they represent independent variation. While expected earnings are related to college major choices, the experimental measures are not related with college major choice.
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Turf wars in organizations commonly occur in environments where competition undermines collaboration. We develop a game theoretic model and experimental test of turf wars. The model explores how team production incentives ex post affect team formation decisions ex ante. In the game, one agent decides whether to share jurisdiction over a project with other agents. Agents with jurisdiction decide whether to exert effort and receive a reward based on their relative performance. Hence, sharing can increase joint production but introduces competition for the reward. We find that collaboration has a non-monotonic relationship with both productivity and rewards. The laboratory experiment confirms the model's main predictions.
We use a combination of lab and field evidence to study whether highly-impatient individuals are more likely to procrastinate. To measure impatience, we elicit individual discount rates by giving participants choices between smaller-sooner and larger-later rewards. To measure procrastination, we record how fast participants complete three tasks: an online game, their application to the university, and a mandatory survey. We find that, consistent with the theory, impatient individuals procrastinate more, but only in tasks where there are costs to delay (the online game and university application). Since we paid participants by check to control for transaction costs, we are also able to determine whether the participants' cashing behavior is consistent with the timing of their payment choice. We find substantial evidence of time inconsistency. Namely, more that half of the participants who received their check straight away instead of waiting two weeks for a reasonably larger amount, subsequently took more than two weeks to cash it.
We study the formation of advocacy groups and how they can impact policy outcomes by revealing information about voters' preferences to uninformed political candidates. We conduct a laboratory experiment based on a two-candidate spatial electoral competition setting where the policy preferences of voters are (initially) unknown and change over time. In the control treatment candidates learn about the preferred policy of the median voter through the voting outcome of elections. In the advocacy treatments, voters can organize themselves into advocacy groups in order to reveal their policy preferences. We find that voters often overcome the collective action problem of forming an advocacy group. In fact, we observe the formation of both informative advocacy groups, which convey new information, and uninformative advocacy groups, which do not. Overall, advocacy groups significantly speed up the convergence to the preferred policy of the median voter. However, advocacy does not lead to higher earnings as the gains from faster convergence are offset by the costs of group formation.
We introduce three extensions of the Hirshleifer-Skaperdas conflict game to study experimentally the effects of post-conflict behavior and repeated interaction on the allocation of effort between production and appropriation. Without repeated interaction, destruction of resources by defeated players can lead to lower appropriative efforts and higher overall efficiency. With repeated interaction, appropriative efforts are considerably reduced because some groups manage to avoid fighting altogether, often after substantial initial conflict. To attain peace, players must first engage in costly signaling by making themselves vulnerable and by forgoing the possibility to appropriate the resources of defeated opponents.
Women outnumber men in undergraduate enrollments, but they are much less likely than men to major in mathematics or science or to choose a profession in these fields. This outcome often is attributed to the effects of negative sex-based stereotypes. We studied the effect of such stereotypes in an experimental market, where subjects were hired to perform an arithmetic task that, on average, both genders perform equally well. We find that without any information other than a candidate's appearance (which makes sex clear), both male and female subjects are twice more likely to hire a man than a woman. The discrimination survives if performance on the arithmetic task is self-reported, because men tend to boast about their performance, whereas women generally underreport it. The discrimination is reduced, but not eliminated, by providing full information about previous performance on the task. By using the Implicit Association Test, we show that implicit stereotypes are responsible for the initial average bias in sex-related beliefs and for a bias in updating expectations when performance information is self-reported. That is, employers biased against women are less likely to take into account the fact that men, on average, boast more than women about their future performance, leading to suboptimal hiring choices that remain biased in favor of men.
The ability of groups to implement efficiency-enhancing institutions is emerging as a central theme of research in economics. This paper explores voting on a scheme of intergroup competition which facilitates cooperation in a social dilemma situation. Experimental results show that the competitive scheme fosters cooperation. Competition is popular but also that the electoral outcome depends strongly on specific voting rules of institutional choice. If the majority decides, competition is almost always adopted. If likely losers from competition have veto power, it is often not, and substantial gains in efficiency are foregone.
We investigate the intrinsic motivation of individuals to report, and thereby sanction, fellow group members who lie for personal gain. We further explore the changes in lying and reporting behavior that result from giving individuals a say in who joins their group. We find that enough individuals are willing to report lies such that in fixed groups lying is unprofitable. However, we also find that when groups can select their members, individuals who report lies are generally shunned, even by groups where lying is absent. This facilitates the formation of dishonest groups where lying is prevalent and reporting is nonexistent.
We experimentally study the common wisdom that money buys political influence. In the game, one special interest (i.e., a corporate firm) has the opportunity to influence redistributive tax policies in her favor by transferring money to two competing candidates. The success of the investment depends on whether or not the candidates are willing and able to collude on low-tax policies that do not harm their relative chances in the elections. In the experiment, successful political influence never materializes when the firm and candidates interact just once. By contrast, it yields substantially lower redistribution in about 40% of societies with finitely-repeated encounters. However, investments are not always profitable, and profit-sharing between the firm and candidates depends on prominent equity norms. Our experimental results shed new light on the complex process of buying political influence in everyday politics and help explain why only relatively few firms do actually attempt to influence policymaking.
We study the interaction between competitive markets and income redistribution that reallocates unequal pre-tax market incomes away from the rich to the poor majority. In one setup, participants earn their income by trading in a double auction (DA) with exogenous zero or full redistribution. In another setup, after trading, they vote on redistributive tax policies in a majoritarian election with two competing candidates. This results in virtually full redistribution, even when participants have the opportunity to influence taxes by transferring money to the candidates. We find that the high redistribution reduces trading efficiency, but not as much as predicted if market participants trade randomly. This is because, rather than capitulating to the much lower trading incentives, many participants respond to redistribution by asking and bidding more conservatively in the DA, and in this way help to prevent further efficiency losses.
We investigate the emergence and enforcement of contribution norms to public goods in homogeneous and heterogeneous groups. With survey data we demonstrate that uninvolved individuals hold well defined yet conflicting normative views of fair contribution rules related to efficiency, equality, and equity. In the experiment, in the absence of punishment no positive contribution norm is observed and all groups converge towards free-riding. With punishment, strong and stable differences in contributions emerge across group types and individuals in different roles. In some cases these differences result from the emergence of an efficiency norm where all fully contribute. In the cases where full efficiency is not attained, these differences result from the enforcement of different relative contribution norms. Hence, our experimental data show that, even in heterogeneous groups, individuals can overcome the collective action problem inherent in public good games by agreeing on and enforcing a contribution norm.
We present evidence from an experiment in which groups select a leader to compete against the leaders of other groups in a real-effort task that they have all performed in the past. We find that women are selected much less often as leaders than is suggested by their individual past performance. We study three potential explanations for the underrepresentation of women, namely, gender differences in overconfidence concerning past performance, in the willingness to exaggerate past performance to the group, and in the reaction to monetary incentives. We find that men's overconfidence is the driving force behind the observed prevalence of male representation.
We propose a novel experimental method that disentangles strategically- and non-strategically-motivated behavior. We apply it to an indefinitely-repeated prisoner's dilemma game to observe simultaneously how the same individual behaves in situations with future interaction and in situations with no future interaction, while controlling for expectations. This method allows us to determine the extent to which strategically-cooperating individuals are responsible for the observed pattern of cooperation in experiments with repeated interaction, including the so-called endgame effect. Our results indicate that the most common motive for cooperation in repeated games is strategic.
This article reports results of a field experiment in which two hundred e-mails were sent to authors of recent articles in economics that had promised to send the interested reader supplementary material, such as alternative econometric specifications, “upon request.” The e-mails were sent either by a researcher affiliated at Columbia University, New York or the University of Warsaw, Poland; furthermore, the authors' position (assistant professor) was specified in half the e-mails only. Overall, 64% of the approached authors responded to our message, of which two thirds (44% of the entire sample) delivered the requested materials. The frequency and speed of responding and delivering were very weakly affected by the position and affiliation of the sender. Gender or affiliation of the author, number of citations or journal impact factor or the type of object in question seemed to make no difference. However, authors of published articles were much more likely to share than authors of working papers.
This experimental study investigates how behavior changes after receiving punishment. The focus is on how proposers in a power-to-take game adjust their behavior depending on their fairness perceptions, their experienced emotions, and their interaction with responders. We find that fairness plays an important role: proposers who take what they consider to be an unfair amount experience higher intensities of prosocial emotions (shame and guilt), particularly if they are punished. This emotional experience induces proposers to lower their claims. We also find that fairness perceptions vary considerably between individuals. Therefore, it is not necessarily the case that proposers who considered themselves fair are taking less from responders than other proposers. Lastly, we provide evidence that suggests that eliciting emotions through self-reports does not affect subsequent behavior.
This paper reports a positive and statistically significant relation between short-term discount rates elicited with a monetary and a primary reward (chocolate). This finding suggests that high short-term discount rates are related to an underling individual trait.
We test if cooperation is promoted by rank-order competition between groups in which all groups can be ranked first, i.e. when everyone can be a winner. This type of rank-order competition has the advantage that it can eliminate the negative externality a group's performance imposes on other groups. However, it has the disadvantage that incentives to outperform others are absent, and therefore it does not eliminate equilibria where all groups cooperate at an equal but low level. We find that all-can-win competition produces a universal increase in cooperation and benefits a majority of individuals if the incentive to compete is sharp.
This paper experimentally explores how the enforcement of cooperative behavior in a social dilemma is facilitated through institutional as well as emotional mechanisms. Recent studies emphasize the importance of anger and its role in motivating individuals to punish free riders. However, we find that anger also triggers retaliatory behavior by the punished individuals. This makes the enforcement of a cooperative norm more costly. We show that in addition to anger, "social" emotions like guilt need to be present for punishment to be an effective deterrent of uncooperative actions. They play a key role by subduing the desire of punished individuals to retaliate and by motivating them to behave more cooperatively in the future.
We study experimentally the effect of expectations on whether trust is repaid. Subjects respond with untrustworthy behavior if they see that little is expected of them. This suggests that guilt aversion plays an important role in the repayment of trust.
In public-good provision, privileged groups enjoy the advantage that some of their members find it optimal to supply a positive amount of the public good. However, the inherent asymmetric nature of these groups may make the enforcement of cooperative behavior through informal sanctioning harder to accomplish. In this article, the authors experimentally investigate public-good provision in normal and privileged groups with and without decentralized punishment. The authors find that compared to normal groups, privileged groups are relatively ineffective in using costly sanctions to increase everyone's contributions. Punishment is less targeted toward strong free riders, and they exhibit a weaker increase in contributions after being punished. Thus, the authors show that privileged groups are not as privileged as they initially seem.
This is an experimental study of negative reciprocity in the case of multiple reciprocators. We use a three-player power-to-take game where a proposer is matched with two responders. We compare a treatment in which responders are anonymous to each other (strangers) with one in which responders know each other from outside the lab (friends). We focus on the responders' decisions, beliefs, and emotions. Our main findings are: (1) friends punish the proposer more than strangers, (2) friends are more likely to coordinate their punishment (without communication), and (3) both punishment and coordination are explained by the responders' emotional reactions.
Why humans are prone to cooperate puzzles biologists, psychologists and economists alike. Between-group conflict has been hypothesized to drive within-group cooperation. However, such conflicts did not have lasting effects in laboratory experiments, because they were about luxury goods, not needed for survival (“looting”). Here, we find within-group cooperation to last when between-group conflict is implemented as “all-out war” (eliminating the weakest groups). Human subjects invested in helping group members to avoid having the lowest collective pay-off, whereas they failed to cooperate in control treatments with random group elimination or with no subdivision in groups. When the game was repeated, experience was found to promote helping. Thus, not within-group interactions alone, not random group elimination, but pay-off-dependent group elimination was found to drive within-group cooperation in our experiment. We suggest that some forms of human cooperation are maintained by multi-level selection: reciprocity within groups and lethal competition among groups acting together.
Strategic analysts require a systematic approach to model and analyze their decisions, and firms often turn to game theory when thinking about competitive dynamics. This case gives students a game theory primer by putting them in the role of strategists working for Coca-Cola Enterprises who have been asked to determine how a planned bottling plant in Wisconsin will affect the company's profitability. Students learn the benefits of this approach as a strategic tool, and also explore recent advances in the behavioral aspects of game theory.
This document describes the data analyzed in the Chicago-Templeton longitudinal study. The study is based on the entire 2008 generation of MBA students from the University of Chicago Booth School of Business. The data described in this document are obtained from three different sources: surveys, laboratory experiments, and the school's admission department. We give a brief overview of each data source, in addition to a detailed description of the data-collection procedures.
Fairness norms are an elusive and yet important characteristic of our societies. In many situations of interest to economists, the active enforcement of fairness norms affect behavior in significant ways. This thesis studies the motivations of individuals to comply with and to enforce fairness norms. Furthermore, the circumstances under which the enforcement of fairness norms leads to desirable outcomes are investigated. Particular attention is given to the effects of punishment, fairness perceptions, and emotions on an individual's willingness to behave in a fair manner. Latter chapters study norm enforcement in public good settings. First, in groups with heterogeneous endowments, and second, in groups that have less free riding incentives but suffer from the fact that high cooperation levels are no longer supported by fairness norms.
This paper describes how our understanding of collective action has evolved over the years. I use Olson's model of collective action to relate six essentially different approaches. For each approach, I highlight its contribution as well as its main drawbacks. We still do not have a satisfactory explanation for collective action. However, recent work on cognitively and emotionally bounded agents promises to deliver significant insights.