This chapter explores the impact and the signifi cance of the UK ‘Gender Recognition Act’ (GRA 2004) on trans individuals and trans communities.1 The GRA came into being in 2004; enabling trans people to legally change their birth certifi cates and to marry or civilly partner in their acquired gender. In order to contextualise the GRA within shifting conceptualisations of gender more broadly, the chapter fi rst examines understandings of gender-and of transgender-within feminist, queer and transgender theory. I move on to examine how these theoretical shifts were mirrored in trans activism, and, particularly, evident in the legal challenges brought by trans people, which formed the backdrop to the GRA. Yet, as I explore in my discussion of medical understandings of transsexuality, such conceptual and political frameworks contrast sharply with medical thinking, which is also woven into the GRA. I thus suggest that the GRA embodies on-going tensions between very different ways of understanding (trans) gender.