In the UK, a person is diagnosed with cancer every two minutes and dies from cancer every four minutes. This chapter outlines the development of cancer, types of cancer cells and stages of cancer. It outlines the symptoms of cancer in the lung, breast, prostate, bowel, stomach, pancreas, female reproductive system and skin. The chapter provides an overview of the epidemiology of cancer in the UK, including incidence, survival and mortality data. The causes of cancer are explained as non-modifiable risk factors and modifiable risk factors. The latter examines 11 carcinogens which people could address in order to prevent 40% of cancers. These include tobacco, weight, radiation, occupation, infection, alcohol, diet, physical inactivity, pollution and hormones. The chapter ends with a short description of the secondary and tertiary prevention of cancer, which includes screening and treatment.