This article reviews the current literature characterizing potential factors associated with the etiologies of gender identity. The PubMed database was searched for all literature that assessed key elements affecting development of gender identity. Current models attribute gender identity etiology to endogenous biology along with prenatal androgen exposure. However, no genetic loci or specific neuroanatomic regions have been consistently identified as the single explanation for transgender identity. Although environment may play a role in gender expression, there are no data to suggest an exogenous explanation for the development of gender identity.