This text begins with a general introduction to biochemical and biophysical aspects of circadian timing, then proceeds to its essential focus on collating the newest information on molecular mechanisms of circadian rhythms. It includes a chapter on the implications for clinical research on affective disorders, sleep disorders, and the relevance for therapeutic treatment, as well as coverage of multiple oscillators and hormonal rhythms. Sections include: Molecular Control of Circadian Rhythms: Animal Models Molecular Control of Circadian Rhythms: From Cyanobacteria to Plants Circadian Organization in Complex Organisms. Chapter topics include examinations of circadian rhythms in non-mammalian vertebrates, neurospora, and humans.