LocusLink organizes information from collaborating public databases and from other groups within NCBI to provide a locus-centered view of genomic information from human, mouse, rat, zebrafish, Drosophila melanogaster, and human immunodeficiency virus 1 (HIV-1). Each LocusLink record (one for each locus) consists of a collection of links to more information about a locus. The intent, therefore, is not to copy all information about a locus into one record; the intent is to provide a sufficient description of each linked item so that LocusLink can be searched and to provide enough connections for users to find related resources. As part of this process, a unique integer is assigned to each locus. This identifier can then be used by other resources to connect back to LocusLink.