Steroids are a unique class of chemical compounds found throughout the animal and plant kingdom. This class includes sterols such as cholesterol and ergosterol, bile acids, and steroid hormones. Chemical research on steroids began with isolation and structure determination, and major research efforts focused on total synthesis and on the development of numerous reactions for modifying the steroid scaffold. Methods in microbial transformations of steroids were developed to produce large quantities of steroid starting materials at reduced costs. Research in steroid biochemistry first began with studies on the biosynthesis and metabolism of steroids, followed soon thereafter by investigations on the biochemical mechanism of action of steroids. Over the past several decades, steroid biochemistry and molecular biology have focused on steroidogenic enzymes, nuclear steroid receptors, and gene expression. The discovery of the anti‐inflammatory effects of cortisone in the treatment of rheumatoid arthritis and the report of the contraceptive effects of estrogen and progestin preparations illustrated for the first time that steroids could be considered as medicinal agents. As a result, extensive research on the medicinal chemistry, pharmacology, and clinical studies of steroid agonists and antagonists has evolved and continues to provide new insights and new medicinal agents for therapies in many different diseases and chemoprevention strategies.