This chapter offers an account of central issues and themes in queer theory, with particular attention to the challenges it has posed to the concepts of normativity, identity, and the category of “woman.” It explores queer theory’s emergence from lesbian and gay studies, and considers its relation to feminist philosophy and trans theory. The chapter outlines the founding contributions of Judith Butler and Eve Kosofsky Sedgwick, along with several other influential queer theorists, and traces the concept of heteronormativity from its central place in queer theory’s earliest works to more recent reconsiderations.