The Transgender Women's Internet Survey and Testing (TWIST) study is an annual, cross-sectional online HIV behavioral survey of transgender women and transfeminine non-binary people assigned male at birth in the United States. The study also includes an optional mail-in self-testing kit for HIV/STIs, hepatitis C, and hormone levels (estrogen and testosterone). This study aims to examine the role of gender identity-based and sexual behavior-based stigmas on mental and sexual health, resilience, and access to care in this population.