The global incidence of cancer is expected to increase substantially over the next decades. This trend is very much driven by a rise in lifestyle-related cancers due to economic and demographic transitions worldwide. Lifestyle factors, such as smoking, alcohol consumption, obesity, diet, and physical inactivity, and also reproductive and hormonal factors are considered as causes of cancer and main targets for primary prevention. While smoking, which may be responsible for around 20% to 30% of all incident cancers, is clearly the strongest lifestyle-related risk factor overall, followed by alcohol consumption and obesity, the importance of specific factors for individual cancer types and subtypes varies greatly. Remarkably, it has been argued that half of all cancers in industrially developed and affluent societies could be avoided by nonsmoking, reducing alcohol consumption, weight control and physical activity, a plant-based diet, and breast-feeding.