In the future' the decade of the 1990s will likely be viewed as a Golden Age for retinoid research. There have been unprecedented research gains in the understanding of retinoid actions and physiology; since the retinoid nuclear receptors were first identified and the importance of retinoic acid in developmental processes was first broadly recognized in the late 1980s. Between then and now, our knowledge of retinoid action has evolved from one of a near complete lack of understanding of how retinoids act within cells to one of sophisticated understanding of the molecular processes through which retinoids modulate transcription. In this volume, we have tried to provide a comprehensive update of the present understanding of retinoid actions, with an emphasis on re­ cent advances. The initial chapters of the volume, or Section A, focus on the physicochemical properties and metabolism of naturally occurring retinoids: - N OY provides an uncommonly encountered view of retinoid effects from the perspective of the physiochemical properties of retinoids. - V AKIANI and BUCK lend a perspective on the biological occurrence and actions of retro- and anhydro-retinoids. Section B considers both the retinoid nuclear receptors and their mechanisms of action as well as synthetic retinoids that have been used exper­ imentally to provide mechanistic insights into receptor actions and have potential therapeutic use for treating disease: - PIEDRAFITA and PFAHL provide a comprehensive review of retinoid nuclear receptor biochemistry and molecular biology.