The growing visibility of transgender and nonbinary people raises important sociological questions about how the structure of sex and gender is shifting and underscores necessary changes to research practice. We review what is known about emerging gender identities and their implications for sociological understandings of the relationship between sex and gender and the maintenance of the sex/gender system of inequality. Transgender and nonbinary identities are increasingly common among younger cohorts and improved survey measurements of sex and gender are expanding information about these changes. In the United States, an additional gender category seems to be solidifying in public usage even as the higher status of masculinity over femininity persists. The continuing power of the normative binary contributes to both violent backlash and characteristic patterns of discrimination against gender diverse people; yet, underlying support for nondiscrimination in the workplace is stronger than commonly recognized. New, more consistent efforts to account for gender diversity in social science research are needed to fully understand these changes.