By 2020, the world population is expected to have increased to 7.5 billion; of this number, approximately 15 million new cancer cases will be diagnosed, and 12 million cancer patients will die. Cancer is a genetic disease, but this does not mean that acquiring cancer is just a fatality or bad luck. Actually it is now known that most of the diseases depend on complex interactions between the individual genome and environmental factors that influence the gene expression. Not surprisingly, it has been observed that regular physical activity may play a relevant role in the prevention and treatment of cancer. This book is the result of many years reviewing and researching on this interesting relationship between physical activity and cancer, and may help students, health professionals and researchers to be introduced and updated in this emerging issue.