This text focuses on group behaviour in developing countries. It includes studies of producer and community organizations, NGOs, and some public sector groups. Despite the fact that most economic decisions are taken by people acting within groups - families, firms, neighbourhood or community associations, and networks of producers - the analysis of group functioning has not received enough attention, particularly among economists. Some groups function well, from the perspectives of equity, efficiency, and well-being, while others do not. This book explores why The text covers groups that perform three types of function: overcoming market failures (for example, producer organizations); improving the position of their members (for example, Trade Unions), and distributing resources to the less well-off (for example, NGOs and the public sector) It contrasts three modes of group behaviour: power and control; co-operation; and the use of material incentives, exploring what determines modes of behaviour of groups, and the consequences for efficiency, equity, and well-being.