Public health specialists can be described as leaders of the ‘upstream health workforce’, concerned with preventing unnecessary and ‘revolving door’ contact with health services. Achieving this requires working to promote good health, improve health services and protect populations from infectious disease and environmental risks. Public health work is based upon the recognition that populations are complex constructions of groups of individuals, who may or may not seek help for health problems or be able effectively to take action to improve their own health. This article will define key areas of public health practice giving specific examples of the role of the public health specialist in the UK, as well as how and why primary care professionals might access specialist advice. The examples demonstrate the great potential for improving population health through the complementary efforts of primary care and public health professionals.