Most conservation and development initiatives assume that rules limiting resource extraction are necessary for ecological sustainability. While this is often true, in some social–ecological systems, unpredictable ecosystem dynamics and limited exploitation technology make it unlikely that people will overstep the ecological threshold, precluding the need for management rules. Here, two kinds of systems can emerge: open access systems in which individuals can meet their needs without cooperating with others, and a cooperative open access system in which social rules are required though management rules are not, because individuals need to cooperate to survive and to prevent erosion of cooperation by free-riders. We provide three brief case studies illustrating cooperative open access: Pantaneiro fishers, Agta hunter-gatherers, and Maasai pastoralists. We conclude that understanding these exceptions is pivotal for a better theoretical understanding of social–ecological systems, and can be valuable in building a strategic approach to conservation.