In 1990, an international coalition of scientists successfully argued for huge public investment to support their work to sequence the human genome. Proponents of the Human Genome Project described it at the time as ‘one of mankind’s greatest odysseys. It is a quest that is leading to a new understanding of what it means to be a human being’ (Bodmer and McKie, 1994: vii). According to its advocates, the resulting knowledge of human genetic make-up would not only impact on basic science, the practice of medicine and the delivery of healthcare; it would also do much to explain human behaviour, elucidating and even offering solutions to social problems and reshaping how humans think of themselves and relate to others. The Human Genome Project spurred renewed claims by scientists to speak authoritatively about what makes us who we are, challenging the position held by the social sciences, and in particular by sociology, since the end of the Second World War. Over the past two decades, social scientists from different traditions – sometimes in alliance with sympathetic scientists – have risen to this challenge in two distinct but related ways: first, by engaging with and critiquing claims about the explanatory power of genetics; and second, by studying the myriad ways in which actors draw upon and interpret genetic knowledge as part of their identity-making practices. This latter programme of research and reflection has been particularly fruitful as a source of insights into the sociology of identity. Early fears that genetics would lend itself to a process of reification and standardisation of identities (Flower and Heath, 1993) have been superseded by a growing appreciation of the extent to which ‘individuals resist, appropriate, or accommodate themselves to genetic power/knowledge in line with diverse identity politics, not schemes of centralized or capillary control’ (Brodwin, 2005: 142). Social scientists have accordingly assembled a rich and multifaceted empirical literature on the ways in which identities are formed where genetics comes to be involved. The articles in this Special Issue contribute to this sociological understanding of genetic knowledge and identity practices in two key respects. On the one hand, they emphasise just how deeply genetics has penetrated into many realms of social life. On the other, they illustrate the diversity of the ways in which identities are negotiated between self, others and institutions, and how the language and practices of genetics – and heredity more generally – have been integrated into those negotiations. Before discussing the contributions of the individual articles in this Special Issue, we briefly revisit the wider sociological literature on identity in order to specify the particular challenges raised by these new empirical analyses.