The past several decades have produced a surge of research on the physical and mental health benefits of religiousness and spirituality. This chapter summarizes the results of the research studies and focuses on clinicians’ integration of religiousness and spirituality into practice with patients. This chapter begins by defining religiousness and spirituality, as these definitions have been varied across studies. Next, the evidence for physical and mental health benefits will be summarized. Particular attention will be given to the most common chronic illnesses. Further, theoretical explanations for these relationships will be presented. The majority of this chapter will provide examples of religiousness and spirituality and offer guidelines for clinicians. Also, challenges that may come from the clinician’s own beliefs will be described and the importance of cultural competency will be included. While much of the research highlights positive relationships between health and spirituality, this chapter will also bring awareness to the negative relationships that have been identified. Lastly, barriers to integrating religiousness and spirituality will be addressed. Patients’ spiritual concerns can begin to be addressed by asking a practical question as simple as: “Are there any spiritual or religious beliefs you think are important for me to know to help me care for you better?”