1. Introduction to biological rhythms, their properties, and clock control -- 2. A survey of rhythms in plants and animals -- 3. Tidal (bimodal lunar-day) rhythms -- 4. Human rhythms -- 5. Clock compensated animal orientation -- 6. The clock control of plant and animal photoperiodism -- 7. Evidence for external timing of biological clocks / Frank A. Brown, Jr. -- 8. Models and mechanisms for endogenous timekeeping / Leland N. Edmunds, Jr.