© 2002 by CRC Press LLC. This section deals with thermogenesis, which we define as energy expenditure (EE) above resting metabolic rate (RMR) not associated with physical activity. Other sections in this volume deal with both RMR and physical activity individually, and therefore these subjects will not be addressed. As defined for discussion in this section, thermogenesis can be produced from diet, drugs, and cold exposure. This section will discuss factors that may enhance thermogenesis, followed by a discussion of potential implications of thermogenesis in determining total energy expenditure (TEE), and how modulations in thermogenesis may influence the obesity epidemic now facing the United States and other countries.