Steroid hormones and the secosteroid, vitamin D, belong to an ancient family of signaling molecules with diverse functions, including central roles in the regulation of female and male reproductive processes. The human steroid hormones are derived from cholesterol, an abundant plasma lipid and a structural component of plasma membranes and other organelles. Seemingly subtle modifications of the four fused rings of the sterol skeleton and side chain result in molecules with different and diverse activities. This chapter reviews the general features of the synthesis and metabolism of steroid hormones, the ways in which these processes are controlled physiologically, the ways in which these processes can be modified by pharmacological intervention, and some genetic disorders that interfere with normal steroid synthesis and metabolism.