Science fiction (‘SF’) is often understood as a literature of radical possibilities—but to what extent do SF writers break the mould of humanist thought that has informed much of the western literary and cultural tradition? In this thesis, I will examine the concept of the ‘human’ as it has been incorporated into works of Anglo-American SF from the nineteenth century to the 1970s. By ‘human’, I mean the diverse sets of beliefs, ideas, and qualities attached, consciously or unconsciously, to the terms ‘human’ and ‘humanity’ in these texts. More specifically, I will examine the diverse ways that SF writers have narrativised the human in relation to technology and the natural world. As has been argued by a number of prominent critics, including Donna Haraway, Rosi Braidotti, Cary Wolfe, and Jacques Derrida, attitudes and relationships towards technological systems and material nature have been fundamental in determining the nature and meaning of the ‘human’ in western culture. These critics form part of the field of posthumanism, a branch of critical studies which has been centrally concerned with unearthing, investigating, and challenging what precisely is meant by the terms ‘human’ and ‘humanity’. Deploying a model of posthumanism as a hermeneutical principle for deconstructing the human figure in literary SF, I will stage the argument that, despite the radical ontological and epistemological possibilities generated by SF’s speculative framework, SF texts have been reluctant to embrace models of subjectivity and embodiment that move beyond the narrow humanist tenets of scientific rationalism, biological and material transcendence, teleological progressivism, and instrumentalist views of nature. Through an analysis of a range of human ‘archetypes’ found throughout the history of the genre, I will argue that SF has instead consistently deployed a liminal conception of the human that is ambiguously situated between ‘assimilative’ humanist and ‘transformative’ posthumanist conceptions of the human and nonhuman subject.