The purpose of this research protocol is to screen and enroll individuals who have bipolar disorder and to track each person's course of illness in order to study the long-term course of illness and to elucidate possible clinical and biological predictors of acute and sustained treatment response. As a part of this protocol, subjects will: systematically be administered psychiatric rating scales such as the life-chart method (LCM) for daily assessment of mood, sleep, and behavior; be asked to participate in non-invasive research procedures, such as blood drawing for measurement of thyroid antibodies and intracellular calcium; and be medicated as is clinically appropriate. This protocol also serves as a stepping stone to other protocols such as the comparative acute and long-term efficacy of three antidepressants (#95-M-0129), and the efficacy of omega-3 fatty acids (#00-M-0004), for which separate written informed consents are obtained. Patients in this study are participants in the larger NIMH-Stanley Foundation Bipolar Network (SFBN), which involves six academic sites focused on better understanding the long-term course and treatment of the illness. The current protocol thus serves as an entry point for individuals with bipolar disorder for screening and detailed longitudinal assessment both prior to and in between more formal blind randomized IRB approved treatment protocols.