The articel developes the concept of collective action and argues for the central significance of this concept in order to explain diverse social phenomena, for example the so-called collective dilemmas discussed in game theory, and especially the genesis of social structures. The basic idea is that collective action is more fundamental than social action. First of all, the distinction between collective and social action is defined as a difference which consists in different underlying forms of cooperation. Consistent with this, an analysis of collective or we-intentions is given which has three features: the content of the we-intention is a specific we-representation, the intention has a specific relational property, and it presuppose a specific readiness to cooperate. Finally, it is argued that these characteristics can explain how the genesis of social structures is possible at all.