Despite the difficulty in clearly defining and measuring spirituality, a growing literature describes its importance in oncology and survivorship. Religious/spiritual beliefs influence patients' decision-making with respect to both complementary therapies and aggressive care at the end of life. Measures of spirituality and spiritual well-being correlate with quality of life in cancer patients, cancer survivors, and caregivers. Spiritual needs, reflective of existential concerns in several domains, are a source of significant distress, and care for these needs has been correlated with better psychological and spiritual adjustment as well as with less aggressive care at the end of life. Studies show that while clinicians such as nurses and physicians regard some spiritual care as an appropriate aspect of their role, patients report that they provide it infrequently. Many clinicians report that their religious/spiritual beliefs influence their practice, and practices such as mindfulness have been shown to enhance clinician self-care and equanimity. Challenges remain in the areas of conceptualizing and measuring spirituality, developing and implementing training for spiritual care, and coordinating and partnering with chaplains and religious communities. CA Cancer J Clin 2013;63:280–289. ©2013 American Cancer Society.