The vast majority of people worldwide are religious, but religions are enormously diverse. Psychiatric research has attended more to the paths that people take in pursuit of the special things that religion represents than it has to religion itself. Religion is generally supportive of good mental health, and facilitates coping with illness and adversity, but religious and spiritual struggles (e.g., anger towards God, demonic attributions, religious conflicts, guilt and doubt) can impair mental well-being. Religious experiences, both positive and negative, can be mistaken for psychopathology and therefore need to be taken into account in diagnosis, but a differential diagnosis between spiritual/religious experience and mental disorder is not always helpful. It is possible both to be having a meaningful religious experience and to be suffering from a diagnosable mental disorder. Good clinical practice requires an ability to talk with patients in a sensitive and respectful way about their religious concerns.