Personal responsibility for health has been a topic of debate and analysis for decades. Most publications on the topic are devoted to the ethical and regulatory implications of holding individuals responsible for their own health status. This chapter introduces and discusses a philosophical definition of personal responsibility for health, as part of a logical and semantical analysis of the concept. Responsibility is defined as a relation among six variables U, V, W, X, Y, and Z: U is responsible to V for W to an extent of X and with regards to the time frame Y because of certain normative standards Z. Each of the variables is explained and discussed throughout the chapter. The chapter closes by drawing out the ethical and political implications of such a philosophical model of patients' responsibility for their own health.