Despite social work's commitment to diversity and social justice, anti‐oppressive practice in relation to sexuality is afforded little attention in key texts. In comparison to other social divisions, there appears to be little theoretical analysis of lesbian, gay and bisexual (LGB) oppression and few practice models. Drawing on Thompson's work, a framework for understanding the processes and structures which maintain sexuality oppression is proposed. This analysis identifies the legal, social and political inequalities in the everyday lives of LGB people. The paper examines how heterosexism can help to theorise LGB oppression and aims to translate the term into its ‘full richness’ by using three conceptual domains: normalising heterosexuality, compulsory heterosexuality and intersections with other oppressions. (i) The family is a key site in which heterosexuality is normalised. Children and family social workers are likely to encounter a range of beliefs in which LGB families are constituted as inferior: children lack appropriate gender role models, children will grow up gay, children of same‐sex parents are bullied and gay men are a threat to children. (ii) The compulsory status of heterosexuality has depended on the erasure of LGB existence: sexuality issues are not addressed in the academic or practice curriculum; LGB people are represented as ‘just the same’ as heterosexuals (services which meet their needs and circumstances are not considered); and LGB service users remain invisible to social workers. (iii) Heterosexism intersects with racism, sexism and disabilism in processes which include othering, treating everybody the same and invisibilisation. This paper offers a theoretical foundation for heterosexism on which emancipatory practice with LGB people can be developed.