Bipolar disorder is a common, recurrent, often severe psychiatric illness that, without adequate treatment, is associated with high rates of morbidity and mortality (Goodwin and Jamison 2007). In the Global Burden of Disease survey, bipolar disorder was the sixth leading cause of disability worldwide in 1990 and, without improved access to treatment, was projected to remain so well into this century (Murray and Lopez 1996). Morbidity from bipolar disorder often extends well beyond manic, hypomanic, mixed, and depressive episodes. Full recovery of functioning can lag many months behind symptomatic improvement, and repeated episodes can lead to lasting functional impairment (Judd et al. 2005). Recent naturalistic outcome studies indicate that many patients with bipolar disorder spend protracted periods of time neither well nor syndromally ill but rather suffering from chronic subsyndromal, especially depressive, symptoms (Judd et al. 2002, 2003). Bipolar disorder is also among the most heritable of all medical illnesses (Goodwin and Jamison 2007).