"Many important social problems—from the workplace to climate change—require the cooperation of individuals in situations in which collective welfare is jeopardized by self-interest and contractual solutions that align collective and individual interest are not feasible. While this suggests a bleak outcome if people are selfish, recent research in the behavioural sciences suggests that rather than being selfish, many people are non-strategic ‘strong reciprocators’ who cooperate if others cooperate and who punish unfair behaviour even if such cooperation or punishment is individually costly. The fundamental importance of strong reciprocity is that is helps achieving cooperation in situations in which self-interest predicts its breakdown.The major ambition and innovation of this research programme is to “put strong reciprocity into context” by investigating how incentives, social and cultural context, and gender and personality differences, shape strong reciprocity and, as a consequence, cooperation.I propose four linked work packages, which all address key open questions of interest to economists and other behavioural scientists. First, I investigate how incentives influence strong reciprocity: Under which conditions do incentives undermine or enhance strong reciprocity and thereby cooperation? Second, I investigate how strong reciprocity relates to social norms of cooperation and is shaped by social context. Third, I use cross-cultural experiments to study the role of cultural influences on strong reciprocity and how culture interacts with incentive structures: when does culture matter for cooperation? Finally, I study personality and gender differences in strong reciprocity.All projects use economic experiments and insights from across the behavioural sciences. The overarching objective is to develop a ‘behavioural economics of cooperation’, that is, the basic science of relevant behavioural principles that are needed to achieve sustainable cooperation."