Diverse psychological, interpersonal, environmental, and pharmacological factors that appear to trigger the onset of mania could act via their capacity to cause sleep deprivation, a mechanism that has been shown in experiments with bipolar patients to induce transient or sustained switches into mania. Since mania in turn causes insomnia, the development of mania is potentially self-reinforcing and could become autonomous after being initiated by precipitating factors. The sleep reduction model is based on experimental evidence and is a parsimonious explanation for the precipitation of manic episodes by a wide variety of factors. Furthermore, this model has clear implications for the prevention and treatment of mania and provides a conceptual focus and an experimental paradigm for psychological investigations of the causes of mania.