Everyone has a gender identity. For cisgender people it matches the sex they were assigned at birth; for transgender and nonbinary people it does not. Gender expression, such as clothing or voice, is separate again and does not always signal someone's identity.
US law has moved unevenly on gender identity. In Bostock v. Clayton County in 2020, the Supreme Court ruled 6 to 3 that firing someone for being transgender is sex discrimination under Title VII of the Civil Rights Act of 1964. In January 2025, an executive order directed federal agencies to define sex as fixed at birth and to stop recognizing gender identity in federal policy and documents.
Gender categories have also been shaped by race. Colonizers often imposed a strict two-gender system on Indigenous peoples, and Black women have historically been judged as less feminine under white standards. Understanding gender identity is part of understanding how power sorts people.