There is mounting evidence that cancer survivors who adopt a healthy lifestyle-for example, by exercising, consuming a healthy diet, and not smoking-reap physical and emotional benefits. Depending on the behavior targeted, these benefits may include reduced fatigue, improved physical functioning, improved (patio) of life, and greater likelihood of disease-free survival. Given the advantages, cancer survivors should be urged to address any unhealthy behaviors. It remains unclear, however, when cancer survivors will be most receptive to advice from health care providers and others about their lifestyle behaviors. In other words, it is unclear if a "teachable moment" occurs shortly after the cancer diagnosis, during cancer treatment, or sometime after treatment has been completed. This review describes the reasons it has been difficult to identify the optimal time within the cancer trajectory to promote healthy lifestyle behaviors. Some strategies for clarifying the optimal timing are discussed. The review concludes by summarizing health behavior recommendations for cancer survivors outlined by an American Cancer Society expert panel.