Recently, scholars from a variety of disciplines have begun to investigate passionate love, sexual desire, and sexual behavior. Specifically, they have started to ask such questions as: ''Why do young men and women engage in sexual liaisons?'' ''Why do they avoid such encounters?'' Unfortunately, in attempting to answer such questions, scholars have generally focused on surveys and experiments within their own disciplines and have accorded scant attention to the discoveries of other disciplines. In this paper, we will begin by discussing three theoretical perspectives that have had the most to say about why young people seek out (or avoid) sex-cultural psychology, evolutionary psychology, and social psychology (where theorists often take a biopsychosocial approach). Then, we will (1) describe the many scales that have been used to assess sexual motives, and (2) review the multidisciplinary data which has been assembled in an attempt to answer the questions as to why people seek out (or avoid) sexual activity. Unfortunately, almost all this research was conducted by Western researchers, investigating the attitudes and behavior of young American men and women, who were heterosexual. (Alas, the wider-ranging data one would wish to consider is as yet only rarely available.) Through this multidisciplinary synthesis, we hope to demonstrate the impact of culture, social experience, and biological imperatives in shaping young men's and women's motives for engaging in sexual encounters and provide a sort of ''encyclopedia'' of sexual motives measures and research for future scholars.