This chapter explains why a focus on difference and diversity is needed, relating this to work in sexuality studies and gerontology. It outlines theories concerning individual, social and cultural diversity. The chapter draws on theories of intersectionality, explaining where they emanate from, what they add to questions of difference, and why they are useful to help us make sense of the lives and experiences of older lesbian, gay and/or bisexual (LGB) people. It draws on different elements of the discussion together, making the case for the need to address the complexity and multidimensionality of LGB ageing. The diversity theories has illustrated that any investigation of ageing that fails to fully incorporate individual, social and cultural diversity is fatally flawed, an argument that can be extended to both the development of social policy and the delivery of service provision. Intersectionality was introduced into feminist scholarship in the context of Black feminism and its critique of mainstream feminist and anti-racist theories.