We suggest that a third revolution alongside the better known economic and political ones has been vital to the rise of modernity: the reproductive revolution, comprising a historically unrepeatable shift in the efficiency of human reproduction which for the first time brought demographic security. As well as highlighting the contribution of demographic change to the rise of modernity and addressing the limitations of orthodox theories of the demographic transition, the concept of the reproductive revolution offers a better way to integrate sociology and demography. The former has tended to pay insufficient heed to sexual reproduction, individual mortality and the generational replacement of population, while the latter has undervalued its own distinctive theoretical contribution, portraying demographic change as the effect of causes lying elsewhere. We outline a theory of the reproductive revolution, review some relevant supporting empirical evidence and briefly discuss its implications both for demographic transition theory itself, and for a range of key social changes that we suggest it made possible: the decline of patriarchy and feminisation of the public sphere, the deregulation and privatisation of sexuality, family change, the rise of identity, ‘low’ fertility and ‘population ageing’.