Regardless of their cultural background, people desire to form and maintain relationships with others. Satisfying this need for social acceptance and relatedness makes people happier, whereas social rejection elicits negative feelings. This chapter will first describe several theoretical perspectives on affiliation motivation. Its main focus is directed toward approaches of personality and motivational psychology. For this purpose, different types of motives (implicit vs. explicit) and different facets of affiliation motivation (affiliation and intimacy) will be distinguished. The chapter will close with some recent findings on affiliation motivation and open questions for future research.