Sociality exists in an extraordinary range of ecological settings. For individuals to accrue the benefi ts associated with social interactions, they are required to maintain a degree of spatial and temporal coordination in their activities, and make collective decisions. Such coordination and decision-making has been the focus of much recent research. However, eff orts largely have been directed toward understanding patterns of collective behaviour in relatively stable and cohesive groups. Less well understood is how fi ssion -fusion dynamics mediate the process and outcome of collective decisions making. Here, we aim to apply established concepts and knowledge to highlight the implications of fi ssion -fusion dynamics for collective decisions, presenting a conceptual framework based on the outcome of a small-group discussion INCORE meeting (funded by the European Community ' s Sixth Framework Programme). First, we discuss how the degree of uncertainty in the environment shapes social fl exibility and therefore the types of decisions individuals make in diff erent social settings. Second, we propose that the quality of social relationships and the energetic needs of each individual infl uence fi ssion decisions. Th ird, we explore how these factors aff ect the probability of individuals to fuse. Fourth, we discuss how group size and fi ssionfusion dynamics may aff ect communication processes between individuals at a local or global scale to reach a consensus or to fi ssion. Finally, we off er a number of suggestions for future research, capturing emerging ideas and concepts on the interaction between collective decisions and fi ssion -fusion dynamics.