A diagnosis of cancer may evoke concerns relating to life’s meaning and ultimate purpose that by consensus understanding are considered “spiritual.” In addressing these, oncologists face three tasks: to acknowledge spiritual questions, to recognize spiritual concerns, and to engage with patients about spiritual issues in a supportive way. Some Americans turn to religion to answer spiritual questions, but others are religiously unaffiliated and consider themselves “spiritual but not religious.” Patient spirituality resists ready transformation into quantitative measures. Still, investigators have devised validated instruments that measure spiritual well-being and spiritual needs. Patients’ underlying spiritual belief system and spiritual support network may influence decisions about cancer treatment. Spiritual needs are common among patients with cancer and may affect satisfaction with care. Additional research into how best to measure patient spirituality and to train physicians and nurses to identify and meet patient spiritual needs may improve the overall quality of oncology care.