This lecture introduces the basic concepts of health, disease and illness, words you will hear a lot in your professional career. It is worth thinking about what people mean when they use them. Why? Because how we think about these concepts determines what we will do when we meet them. In other words, how we conceptualize disease determines how we go about responding to it. It is vital that in the early stage of your medical education you develop an historically accurate picture of why medicine has come to be the way it is and why people might behave in the ways that they do regarding health, illness and disease.