The objective of the Public Health Classifications Project is to 'develop and endorse a higher-level classification that captures the breadth and scope of public health activity and provides a unified framework for multiple uses'. Such a unified framework will assist in improving the quality and consistency of reported information on public health activity, performance, expenditure and investment. This report is the output of phase one of the Public Health Classifications Project. It introduces the concept of a multi-dimensional public health classification and describes the challenges encountered in its development. It presents version one of a public health classification, outlines some potential practical applications, and proposes the next steps for phase two of the project.