The field of nutritional oncology aims to modify the environmental factors influencing the genetic changes and their expression at every stage of carcinogenesis, from the initiation of the cancer cell to its metastatic spread to other areas of the body. This text considers the biology of nutrition, evidence from the nutritional epidemiology of cancer, biological approaches to investigating cancer, gene-nutrient interaction, bioactive food components, the nutritional assessment and support of the cancer patient, and the problem of implementing nutrition in guidelines and clinical practice.