This thesis seeks to examine the appropriate role of individual behaviour and responsibility in relation to cancer and weight-control policy in German and US health care systems. It contains six main parts. The first describes and compares the ways in which personal responsibility features in law and policy in both countries. It analyses salient differences in underlying motivation and characterization and highlights ethical tensions that arise from these provisions and their implementation. The second part reviews what established normative theories can do to address the issues that have been identified. It argues that these frameworks lack specificity and are ill-suited as a basis for policy in pluralist societies. It provides an analysis of different notions of the concept of personal responsibility, and makes a proposal for an overarching framework, adopting a procedural justice account that draws on work by Norman Daniels, Jim Sabin and Thomas Scanlon. The third part systematically reviews survey literature on the proper role of personal responsibility and develops an instrument for semi-structured interviews with physicians and population-level surveys in the US and Germany. The instrument complements this earlier survey work and explores key themes that arose in the analysis of policy documents and the philosophical literature. Based on this instrument, the fourth part analyses the findings from twenty semi-structured interviews with primary care physicians and oncologists in Berlin, Germany and Philadelphia, USA. The fifth part presents findings from three population level surveys of 1,000 respondents each. Two surveys with identical instruments were conducted with nonprobability samples (census-adjusted proportional quota sampling with regard to income) in Germany and the US, and one, using a subset of questions, was administered to a probability-based sample in the US. Findings are discussed comparatively between countries and in view of the interviews with physicians. The last part concerns the policy implications of the analysis, and applies the framework proposed in the thesis to the case of colon cancer screening. It seeks to defend an incentive policy that attaches financial advantage to attending counselling on the advantages and disadvantages of colon cancer screening, building also on findings from the surveys, and interviews with physicians. The final chapter highlights a range of general policy implications for the evaluation and implementation of programmes seeking to incentivise personal responsibility.