Strong Reciprocity and Participatory Forest Management in Ethiopia Devesh Rustagi*, Stefanie Engel*, Michael Kosfeld** Abstract Recent research suggests that the power of conditional cooperation norm and punishment of norm violators in sustaining cooperation depends on behavioral type composition of a group, which has been shown, experimentally, to have a predictive effect on cooperation outcome. However, because the existing evidence is exclusively based on experiments with a handful of students from the industrialized west, fundamental questions on the occurrence of this evidence across cultures, in a real world setting, and its policy relevance remain unanswered. Here, we report results from experiments and surveys with 679 members belonging to 49 forest user societies engaged in the management of common property forests in Ethiopia. We find that, first, 35 % members behave as conditional cooperators. Second, the share of conditional cooperators in a society has a significantly positive effect on the society’s forest management outcome, even when we control for the structural determinants of cooperation. Third, conditional cooperators use costly monitoring as a mechanism to achieve a better forest outcome. The unique field settings allow us to generate this evidence in conditions where endogenous group formation, high migration and reverse causality have been ruled out. Our findings provide empirical support to the models of co-evolution of punishment and cooperation. Keywords: Conditional Cooperation, Public Goods Game, Participatory Forest Management, Tragedy of the Commons, Ethiopia. For a full copy of the paper please contact Devesh Rustagi at email@example.com. * Institute for Environmental Decisions, ETH Zurich. Corresponding author (as regards EAERE presentation): Stefanie Engel, Professor of Environmental Policy and Economics, ETH Zurich, Email: firstname.lastname@example.org. ** Goethe University Frankfurt.