Book excerpt: This volume summarizes and organizes a growing body of research supporting the role of motivation in adaptive and rewarding interpersonal interactions with others. The field of human motivation is rapidly growing but most studies have focused on the effects of motivation on individuals' personal happiness and task engagement. Only recently have theorists and empiricists begun to recognize that dispositional and state motivations impact the ways individuals approach interpersonal interactions. In addition, researchers are now recognizing that the quality of interpersonal interactions influences consequent happiness and task engagement, thus helping to explain previous findings to this end. Similarly social psychology and relationships researchers have focused on the impact of cognitions, emotions, and behaviors on people's relationships. In their work, relationships researchers demonstrate that both contextual characteristics and individual differences influence the quality of interactions. Many of these studies seek to understand which characteristics strengthen the bonds between people, encourage empathy and trust and create a sense of well-being after a close interaction. This work seeks to integrate the field of human motivation and interpersonal relationships. Both fields have seen extensive growth in the past decade and each can contribute to the other. However, no single compiled work is available that targets both fields. This is the case, in part because only now is there enough work to make a strong and compelling case for their integration. In the previous years, research has been conducted to show that motivation is relevant and important for interactions among strangers and in close relationships. In addition developmental mechanisms for these relations are identified and mechanisms by which motivation strengthens people's relationships. Finally recent work has demonstrated the many implications for interpersonal relationships, showing that motivation impacts a range of interpersonal processes from prejudice regulation and objectification of others to empathy and care. This book seeks to summarize and organize all these findings and present them in a way that is relevant to both motivation researchers and social and relationship researchers.