The daf-12 gene acts at the convergence of pathways regulating larval diapause, developmental age, and adult longevity inCaenorhabditis elegans. It encodes a nuclear receptor most closely related to two C. elegans receptors, NHR-8 and NHR-48,Drosophila DHR96, and vertebrate vitamin D and pregnane-X receptors. daf-12 has three predicted protein isoforms, two of which contain DNA- and ligand-binding domains, and one of which contains the ligand-binding domain only. Mutations cluster in DNA- and ligand-binding domains, but correspond to distinct phenotypic classes. DAF-12 is expressed widely in target tissues from embryo to adult, but is upregulated during midlarval stages. In the adult, expression persists in nervous system and somatic gonad, two tissues that regulate adult longevity. We propose that DAF-12 integrates hormonal signals in cellular targets to coordinate major life history traits.