Households are groups of people that co-reside and share some resources. Families are households of related individuals. Household and family demography is the study of these primary social groups or social units, and in particular of group membership and the relationships between members of the group. The concepts of household and family depend on cultural, social and economic factors that vary in time and between countries. The conceptual and measurement issues that result are addressed in the chapter. The documentation of changes in households and families and the modelling of these changes represent major challenges in demography. To capture the complexity of households, tabulations of the full array of household relationships replace tabulations of household positions relative to the household head. Household models follow a similar path. Headship rate models that describe household structures from the perspective of the head of household are increasingly being replaced by dynamic models that focus on relationship among members of a household. As a consequence, models of household dynamics change in the direction of models that describe the demographic dynamics of kinship. The chapter reviews the different approaches to the demographic study of households and families, discusses strengths and weaknesses of models, and proposes agent-based models for the description and projection of households and families in varying contexts.