This chapter analyzes the biological underpinnings of male sexual behavior. Research in human sexual behavior has been primarily focused on the effects of pharmacological agents, especially those acting on the serotonergic system and agents that affect the production and action of sex hormones. More recently, brain-imaging studies have increased the understanding of the brain regions and circuits that may underlie sexual desire, arousal, and behavior. The chapter reviews some of these studies, with particular emphasis on the role of the mesolimbic reward system in influencing sexual behavior. In addition to discussing neurobiological contributors to the intensity of the sexual drive, it also describes some work that suggests an association between certain neuroimaging findings and pedophilia. For many years, there has been an understanding of the role of sex hormones in human sexual behavior. Sexual drive and sexual behavior in general are dependent on the levels of these sex hormones. In general terms, androgens are important for the maintenance of sexual behavior in males.