This chapter assesses the relevance of the collective model for the analysis of households in poor countries. As an economic unit, a household creates the possibility of mutual gains for spouses thanks to the possibility of joint consumption of public goods, risk sharing, etc. The collective model assumes that households behave efficiently, in the sense that there is no misallocation or waste of household resources, given the outside options of each spouse. This chapter bridges the theoretical literature describing efficient intra-household behaviour and the development literature that collects empirical regularities pointing toward the existence of strategic decision making among spouses. It examines the key elements of the collective model and discusses its relevance to analysing intra-household behaviour in poor countries. It explores the role that risk and uncertainty, information asymmetries, power imbalances, arranged marriages, strategic investment, gender norms, and extended households play in the attainment of efficiency.