Sleep disturbance has long been recognized as an essential aspect of bipolar disorder. The relationship between sleep and the manic phase of bipolar illness involves the following aspects: decreased need for sleep is a marker of mania; sleep deprivation can induce mania; sleep duration may predict manic episodes; and sleep time may be a marker of response in mania. Although less is known about sleep disturbance in bipolar as compared to unipolar depression, this chapter highlights the phenomenology of sleep in bipolar depression and the potential of sleep deprivation as a theraputic strategy in the depressive phase of bipolar illness. Euthymia, the absence of mood symptoms sufficient to warrant the diagnosis of a depressive, hypomanic, or manic episode, is the goal of treatment of bipolar disorder. It has long been appreciated that bipolar disorder tends to run in families, suggesting it is a heritable disorder.