Our laboratory is interested in understanding how one of the earth’s basic physical features, the day/night cycle, impacts motivated behaviors such as drug seeking. Studies in many species, including humans, have provided clear evidence that the body’s circadian clock is important for organizing behavior patterns to coincide with specific portions of the daily light/dark cycle. Indeed, destruction of the body’s clock or alterations in the fraction of light to dark to which rats are exposed both cause alterations in drug-seeking behaviors. Furthermore, an individual’s chronotype (i.e., the genetically determined propensity to be more alert in the morning vs. evening) is implicated in one’s propensity to become addicted to drugs. Thus, revealing the mechanisms involved in the integration of light/dark with daily behavior patterns could result in novel approaches for the treatment of addiction in a society where efforts to ignore these environmental cues and genetic predispositions together with increased shift work are becoming more common.