Public health is a term much used in the media, by health professionals, and by activists. At the national or the local level there are ministries or departments of public health, whilst international agencies such as the World Health Organisation promote public health policies, and regional organisations such as the European Union have public health funding and policies. But what do we mean when we speak about 'public health'? In this Very Short Introduction Virginia Berridge explores the areas which fall under the remit of public health, and explains how the individual histories of different countries have come to cause great differences in the perception of the role and responsibilities of public health organisations.--