While social network structures are thought to promote cooperation through reputation effects, as suggested by Raub and Weesie (1990), the option of partner choice may undermine these reputation effects in networks. This article approaches this dilemma by comparing the effects of partner choice and reputation diffusion in isolation as well as in combination in a controlled experimental setting. While we do not find that cooperation rates in the absence of partner choice are higher in the presence of reputation effects, we find that emerging cooperation levels near the end of the game are higher when initial cooperation levels are higher. This is more in line with predictions of models of cooperation that rely on learning heuristics rather than forward-looking rationality (i.e., Corten and Cook, 2009). Moreover, we find that the option of partner choice lowers cooperation rates in the absence of reputation effects. However, we do not find a similar effect in the presence of reputation effects. We position these findings in the larger literature on the conditions for cooperation in dynamic societies. Cooperation is a cornerstone of human societies (e.g., Bowles and Gintis 2013; Pennisi 2005; Ostrom 1990). In many instances of social interaction, people join forces to achieve something they could not have achieved alone. Achieving cooperation, however, is often problematic: actors may face incentives to free-ride on the efforts of others, with the result that cooperation never materializes and the payoff to all actors involved is lower than it would have been, had they cooperated. Consider, for example, two researchers who can collaborate on a project, but are also tempted to let the other do most of the work and focus on their individual projects. This situation is formally captured for two actors in the famous Prisoner's Dilemma (PD). 1 The question as to under which conditions cooperation between rational, selfish actors becomes more likely is one of the major problems of the social sciences, and is also known in sociology as the problem of social order (Parsons, 1937). A key finding in this line of research is that cooperation is possible if interac