The process of gender identity development remains poorly understood. Higher prevalence of gender nonconforming identity has been reported in individuals with congenital adrenal hyperplasia, androgen insensitivity syndromes, defects in androgen biosynthesis, and structural differences in sex development, indicating that prenatal and postnatal androgen exposure plays some role in the development of gender identity. Additionally, genetics are thought to play an important role in gender identity based on the observed concordance of gender incongruence in monozygotic twin pairs and reported co-occurrence of gender nonconformity in families. Also, gender identity variance has been associated with distinct morphological characteristics of specific neuroanatomical structures, such as the interstitial nucleus of the anterior hypothalamus 3 and the central part of the bed nucleus of the stria terminalis, supporting the hypothesis that gender identity evolves as a consequence of the interaction of the developing brain and sex hormones. Gender identity development is complex and most likely stems from an intricate interaction between biological, genetic, social, and psychological factors.