My intellectual affinities lie at the border between philosophy, game theory and psychology. My primary research focus is on judgment and decision making with special interest in decisions about fairness, trust, and cooperation, and how expectations affect behavior. A second research focus examines the nature and evolution of social norms, how to measure norms and what strategies to adopt to foster social change. This research is more applied, and forms the core of the newly created Penn Social Norms Group (PennSONG). A third, earlier research focus has been the epistemic foundations of game theory and how changes in information affects rational choices and solutions.

• In my work on norms, I have designed behavioral experiments aimed at testing several hypotheses based on the theory of social norms that I developed in my book, The Grammar of Society: the Nature and Dynamics of Social Norms (Cambridge University Press, 2006). The experimental results show that most subjects have a conditional preference for following pro-social norms. Manipulating their expectations causes major behavioral changes (i.e., from fair to unfair choices, from cooperation to defection, etc.). One of the conclusions we may draw is that there are no such things as stable dispositions or unconditional preferences (to be fair, reciprocate, cooperate, and so on). Another is that policymakers who want to induce pro-social behavior have to work on changing people's expectations about how other people behave in similar situations. These results have major consequences for our understanding of moral behavior and the construction of better normative theories, grounded on what people can in fact do.  

• My consulting and training work with UNICEF, the Gates foundation, the World Bank, DFID and other organizations led me to develop measures of social norms in the field. Sanitation and corruption are two major consulting areas. Most of my group's consulting work consists in developing specific measures, advising on effective interventions, and monitoring sustainability. I have developed a Penn-UNICEF Coursera on Social Norms, and my new book, Norms in the Wild: how to Diagnose, Measure and Change Social Norms (Oxford University Press, 2016) collects my thoughts and experiences from the field work I have been engaged in.    

• The nature and dynamics of social norms studies how norms may emerge and become stable, why an established norm may suddenly be abandoned, how is it possible that inefficient or unpopular norms survive, and what motivates people to obey norms. In order to answer some of these questions, I have combined evolutionary and game-theoretic tools with models of decision making drawn from cognitive and social psychology. A recent interest is modeling the role of trendsetters in social change, and how trendsetters' characteristics interact with social structures.

• My earlier (but never completely abandoned) research focus was the epistemic foundations of game theory. I am presently working on modeling normative expectations, and equilibria based on them. In my past work, I have analyzed the consequences of relaxing the 'common knowledge' assumption in several classes of games. My contributions include axiomatic models of players' theory of the game and the proof that -- in a large class of games -- a player's theory of the game is consistent only if the player's knowledge is limited. An important consequence of assuming bounded knowledge is that it allows for more intuitive solutions to familiar games such as the finitely repeated prisoner's dilemma or the chain-store paradox. I have also been interested in devising mechanical procedures (algorithms) that allow players to compute solutions for games of perfect and imperfect information. Devising such procedures is particularly important for Artificial Intelligence applications, since interacting software agents have to be programmed to play a variety of 'games'.