Congratulations to Prof. Hans Haller on his new book Groups and Market. In this book Dr. Haller and his long-time collaborator Dr. Hans Gersbach of ETH Zurich organize, summarize and expand on their research on general equilibrium models with multi-member households. Often the economic models treat households like single consumers, although the decisions and well-being of individual members are obviously affected by the composition of their respective households. In turn, the formation of a household and its stability may depend on economic conditions and considerations. Professors Gersbach and Haller link together the formation, composition, decision-making and stability of households. Their more advanced models combine traditional exchange (markets for commodities) and matching (markets for people or partners). Their findings help improve our understanding of the economic aspects of social structure and inform economic policy.