As many as two-thirds of cancer cases are linked to environmental factors such as ultraviolet light, tobacco, infectious agents and chemicals. Many of these can be avoided through lifestyle change, but this isn't the whole story. The environment interacts with our genomes, and the resulting genetic changes ultimately cause cancer. Cancer prevention will only be successful when individual behavior is combined with early medical intervention. What are some successful models, and what are the roadblocks to changing behavior? What are the exciting avenues of research towards cancer prevention agents, and what is the economic and regulatory environment for their development? What do we know about the genetic basis of risk, and how will this be applied for early intervention? Cancer screening has the potential for preventing some cancers, but there have been some controversies about benefits and risks. What are the challenges for population-based screening recommendations?