This article presents a model for research and practice that expands on the biopsychosocial model to include the spiritual concerns of patients. Literature review and philosophical inquiry were used. The healing professions should serve the needs of patients as whole persons. Persons can be considered beings-in-relationship, and illness can be considered a disruption in biological relationships that in turn affects all the other relational aspects of a person. Spirituality concerns a person's relationship with transcendence. Therefore, genuinely holistic health care must address the totality of the patient's relational existence-physical, psychological, social, and spiritual. The literature suggests that many patients would like health professionals to attend to their spiritual needs, but health professionals must be morally cautious and eschew proselytizing in any form. Four general domains for measuring various aspects of spirituality are distinguished: religiosity, religious coping and support, spiritual well-being, and spiritual need. A framework for understanding the interactions between these domains is presented. Available instruments are reviewed and critiqued. An agenda for research in the spiritual aspects of illness and care at the end of life is proposed. Spiritual concerns are important to many patients, particularly at the end of life. Much work remains to be done in understanding the spiritual aspects of patient care and how to address spirituality in research and practice.