In all vertebrates gonadal secretions, through their actions on the central nervous system (CNS), control sex and sex-related behaviors and also regulate production of gonadotropin. Recently, major advances have been made in characterizing the molecular events which underlie these processes. Discussed in this paper are the nature and source of androgens and estrogens; their sites of action within the CNS as determined by steroid implant and autoradiographic studies; some manifestations of brain-steroid interactions, both “triggering” and “organizational”; evidence supporting a conventional genomic mechanism versus alternative modes of action; the critical role of androgen metabolizing enzymes in regulating the quality and quantity of active hormone in close proximity to targets; and some determinants of steroid access to the CNS. Information from nonmammalian vertebrates is reviewed in relation to the major body of knowledge derived from common laboratory species. The intent of this paper is to provide a biological perspective and to stimulate interest in the use of unconventional animal models for future studies.