Epidemiological, experimental, and clinical research has shown that chronic stress and adversity are associated with a wide range of biobehavioral processes that may influence cancer progression. These include neuroendocrine alterations (sympathetic nervous system, hypothalamic pituitary adrenal axis), which can up-regulate inflammation and down-regulate antitumor immunity. Such changes may render immune cells less able to detect and destroy tumor cells and may enhance their ability to promote an inflammatory microenvironment. Additionally, neuroendocrine signaling in the tumor microenvironment may promote tumor growth mechanisms, such as angiogenesis, epithelial mesenchymal transition, invasion, and metastasis. Because modifying biobehavioral stress processes might improve cancer health outcomes, randomized controlled trials have tested interventions that can be considered stress management in patients with different forms of cancer. Many trials demonstrate the physical-, mindfulness-, and cognitive-behavioral therapy–based stress management interventions and pharmacologic blockade of stress-related pathways can affect biobehavioral processes in cancer patients and survivors. Importantly, research has now linked stress management–associated changes in these biobehavioral processes early in treatment with long-term health outcomes in some common cancers. We summarize evidence from basic science studies for these biobehavioral associations in multiple cancer models, and from clinical trials for the efficacy of interventions capable of modulating both psychological and biological processes in cancer patients.