Historically, the reasons people have sex have been assumed to be few in number and simple in nature-to reproduce, to experience pleasure, or to relieve sexual tension. Several theoretical perspectives suggest that motives for engaging in sexual intercourse may be larger in number and psychologically complex in nature. Study 1 used a nomination procedure that identified 237 expressed reasons for having sex, ranging from the mundane (e.g., "I wanted to experience physical pleasure") to the spiritual (e.g., "I wanted to get closer to God"), from altruistic (e.g., "I wanted the person to feel good about himself/herself") to vengeful (e.g., "I wanted to get back at my partner for having cheated on me"). Study 2 asked participants (N = 1,549) to evaluate the degree to which each of the 237 reasons had led them to have sexual intercourse. Factor analyses yielded four large factors and 13 subfactors, producing a hierarchical taxonomy. The Physical reasons subfactors included Stress Reduction, Pleasure, Physical Desirability, and Experience Seeking. The Goal Attainment subfactors included Resources, Social Status, Revenge, and Utilitarian. The Emotional subfactors included Love and Commitment and Expression. The three Insecurity subfactors included Self-Esteem Boost, Duty/Pressure, and Mate Guarding. Significant gender differences supported several previously advanced theories. Individual differences in expressed reasons for having sex were coherently linked with personality traits and with individual differences in sexual strategies. Discussion focused on the complexity of sexual motivation and directions for future research.