"Fishing cooperatives (co-ops) and patron-client relationships are the most common cooperative and noncooperative strategies for self-governance for small-scale fisheries around the world. We studied what drives fishers to choose between these two self-governance arrangements in 12 communities in the Gulf of California, Mexico. The communities depend on similar fishing resources, are located in contiguous portions of the coast, fish roughly the same species, have similar socioeconomic characteristics, and sell to similar markets, yet half of the fisheries are organized around co-ops and the other half work through patron-client arrangements. Using participant observation, in-depth interviews of key informants between 1995-2008, and a survey of 55% of the fisheries in the study area, we found that the presence of high transaction costs of commercialization, the desire to acquire fishing licenses, and the existence of traditions of successful collective action among fishing groups within each community strongly influence fishers??? choices regarding membership in fishing co-ops. We also examined the implications of our findings for conservation of fishing resources. Given that the emergence of co-ops was associated with high transaction costs of commercialization, we hypothesize that cooperative strategies are more likely than patron-client strategies to emerge in communities in isolated locations. In an era of globalization, in which the rate of development and urbanization will increase in coastal areas, patron-client strategies are likely to become more prevalent among fisheries, but such self-governance strategies are thought to be less conducive to conservation behaviors."