This book explores the complex relationship between public health research and policy, employing tobacco control and health inequalities in the UK as contrasting case studies. It draws on extensive qualitative data to demonstrate why it makes more sense to focus on ideas, rather than evidence, as the unit of analysis when studying public health knowledge exchange. The book goes on to outline a four-genre typology of ideas, inspired by the work of Max Weber and Bruno Latour, which helps explain both the disjuncture between health inequalities research and policy and the recent spate of policy activity in tobacco control. It argues that focusing on research-informed ideas usefully draws attention to the centrality of values, politics and advocacy for public health debates.