The evidence bearing on the nature and extent of health inequalities documented globally and in the UK is addressed, twin foci within the UK being (a) associations between socioeconomic classification and health and longevity, and (b) the notion of a 'social gradient'. A consideration of the various 'models' that have been developed by sociologists and their allies - most conspicuously social epidemiologists - to account for (a) and (b) is offered, drawing on government-sponsored commissions and reviews as well as the peer-reviewed literature. This is followed by a portrayal of specifically sociological theories of health inequalities, featuring those that hold social structures as well as cultural shifts in convention and behaviour to be causally efficacious for health inequalities. The summary and conclusions of the review incorporate an outline of pertinent questions the sociological community has so far been reluctant to address and an agenda for future research.