The 2021 census will be the UK's first to include a question about sexual orientation, making the UK the first country in the world to ask about this topic in its national census. Asking about sexual orientation in the census poses several challenges, including issues of intra-household privacy and the difficulty of capturing the complex nature of sexual identities using a single question with tick-box responses. This project will investigate the role of organisations representing LGBT people in the process leading to the addition of this question. Through document analysis and interviews with census officials and LGBT organisations involved in advocating for the addition of the sexual orientation question, the project will explore these advocacy efforts and strategies, and analyse how activists navigate tensions between the practical and symbolic importance of recognising LGBT identities in the census and concerns about privacy and the difficulty of enumerating potentially fluid sexual identities.