We study the emergence of norms of cooperation in experimental economies populated by strangers interacting indefinitely and lacking formal enforcement institutions. In all treatments the efficient outcome is sustainable as an equilibrium. We address the following questions: can these economies...

This paper studies how groups resolve disagreement in lottery choices. In an experiment, subjects submit individual proposals, exchange chat messages, and must reach unanimity. Overall, group choices are more coherent and closer to risk neutrality than individuals’. The proposal of the...

In an experiment, a group of strangers was randomly divided in pairs to play a prisoners' dilemma; this process was indefinitely repeated. Cooperation did not increase when subjects could send public messages amounting to binding promises of future play