This chapter considers conceptual understandings and usage of the terms gender and sex as well as the complexity of gender/sex entanglement in the context of health equity research focused on transgender, nonbinary, and genderdiverse people and populations. The aim is to outline current challenges and barriers to transgender health equity, to provide a broad overview of research frameworks and approaches in this area, and to address pressing questions about how best to defne and operationalize gender, sex, and their entanglement. These terms and concepts require consideration because of their impacts on the design, implementation, and interpretation of research that seeks to advance health justice for transgender people. The frameworks and associated measures most frequently employed rely on distinguishing sex from gender identity to meaningfully include transgender people in research and identify populations for tailored interventions. Attending to gender, sex, and their entanglement in transgender health equity research exposes how biological essentialism is used to oppress transgender people; it also challenges widely accepted approaches to measuring transgender health disparities.