This chapter provides an overview of the theoretical and methodological perspectives underpinning LGBTIQ psychology and considerations for undertaking research with LGBTIQ populations. An overview of five main theoretical approaches (essentialism, social constructionism, critical realism, feminism, and queer theory) is provided, and each is discussed in relation to its implications for understanding LGBTIQ people’s lives and experiences. The construct ‘heteronormativity’ is also introduced. The chapter also introduces a range of overarching methodological approaches used in LGBTIQ psychological research (e.g., experiments, surveys, qualitative studies) and explores the extent to which each had been used for researching LGBTIQ topics. The final section of this chapter focuses on considerations in undertaking research with LGBTIQ populations. Challenges in defining populations of interest, access to and recruitment of participants, and principles for ethical practice with LGBTIQ populations are discussed here.