This essay incorporates a general treatment of social interactions into the modern theory of consumer demand. Section 1 introduces the topic and explores some of the existing perspectives on social interactions and their importance in the basic structure of wants. In Section 2, various characteristics of different persons are assumed to affect the utility functions of some persons, and the behavioral implications are systematically explored. Section 3 develops further implications and applications in the context of analyzing intra-family relations, charitable behavior, merit goods and multi-persons interactions, and envy and hatred. The variety and significance of these applications is persuasive testimony not only to the importance of social interactions, but also to the feasibility of incorporating them into a rigorous analysis.