Bipolar affective disorder is a severe, heritable condition affecting about one percent of the population. The mode of inheritance is poorly understood and probably involves multiple loci of small to moderate effect. Genetic linkage has been reported to a number of chromosomal regions; some findings have been replicated. In 1988 the NIMH began a national archival database to search for susceptibility loci/genes in this condition. Its purpose was to collect a large sample of interviews and cell lines from families suitable for linkage and association studies. Since 1988, the NIMH-IRP has been an active site in this multi-center study. The protocol was originally supervised by Elliot Gershon, MD (1988-July 1998) and Dennis L. Murphy, MD (July 1998 - January 2004). In January 2004, Francis J. McMahon, M.D, took over supervision of the protocol. An expanded Consortium of sites concentrating on families identified through a sib pair was approved in August 1998 by the NIMH Extramural Program (MH 59535) via a competitive application. This Consortium added 450 new families and 2500 cell lines. Cell lines, clinical data, and 2 genome-wide sets of microsatellite genotypes have been made freely available to the scientific community under the auspices of the NIMH Center for Genetic Studies. In 2003, the IRB approved an amendment to expand the ascertainment criteria to include sib-pairs with a diagnosis of bipolar II disorder. Families ascertained in this manner are contributed to a second, large sample being collected in collaboration with The Johns Hopkins University and the University of Chicago, known as the CHIP study. In October 2003, the NIMH Extramural Program approved, via a competitive application, an additional 4 years of support for the Consortium collection, now including 11 extramural sites in addition to the IRP site. In this round, the focus shifted from affected sibling pairs to parent-affected offspring triads, with the goal of accruing a large sample suitable for future association studies. Both the Consortium and CHIP projects have similar study design and essentially identical recruitment, evaluation, and analysis procedures, so both projects are described together in what follows.