We examine the conditions leading social movement organizations to adopt consensus in their internal decision making. To do so, we look at organizations of the Swiss global justice movement, which puts the search for consensus at center stage. Our findings show that the ways in which social movement organizations take decisions and their vision of democracy more generally are not simply a matter of free choice by their leaders and members, but depend on certain organizational characteristics. The most important one is a small organizational size, which is a crucial condition for the adoption of consensus in internal decision making. This condition combines with another one pertaining to the cultural tradition of contention represented by the social movement family to explain consensus. In addition, our findings show that small, transnational organizations following inclusive participatory practices are also more likely to adopt consensus when they make decisions.