An individual’s identity development, including his or her preferred gender identity, is a lifelong process, which starts with the earliest interactions with the world. The concepts of gender identity have been explored, studied, debated, and discussed for decades and are currently going through a resurgence of examination, especially in Western cultures. This chapter provides an overview of gender identity development, beginning with an explanation of terms, followed by an exploration of theoretical perspectives which includes cognitive developmental theory, social learning theory, gender schema theory and feminist theory. Topics include current research and perspectives on how gender identity evolves in children and recent shifts in understanding atypical gender identities, including transgender, gender neutral, and gender fluid identification. Finally, implications and strategies for mental health professionals are discussed, especially related to counseling those who are experiencing conflict or distress surrounding issues of gender and gender identity.