Genetic analysis of circadian behavior in mice has revealed that the molecular basis of circadian clocks involves an autoregulatory transcriptional network that oscillates with a 24-hour periodicity. In mammals, the discovery of “clock genes” led to the realization that circadian clocks are cell autonomous and are expressed in the majority of cells and tissues in the body. The master circadian pacemaker located in the hypothalamic suprachiasmatic nucleus sits at the top of a hierarchy of oscillators in the body, but peripheral oscillators can and do respond to more proximal signals such as nutrients and metabolites. Thus, the “circadian system” in mammals is a multi-oscillatory hierarchy. In addition to controlling the timing of behavior and physiology, the clock gene network interacts directly with many other pathways in the cell. These include metabolism, immune function, cardiovascular function and cell growth to name a few. With respect to metabolism, the timing of nutrient consumption is critical, and we and others have shown that restricting the timing of feeding has many health benefits. The lecture will focus on the importance of circadian aligned feeding as a critical factor for aging, health span and longevity.