To the founding fathers of psychology, spiritual phenomena represented critically important topics for psychological study. Since the early part of the twentieth century, however, psychologists have tended to (a) ignore spirituality; (b) view spirituality as pathological; or (c) treat spirituality as a process that can be reduced to more basic underlying psychological, social, and physiological functions. Fortunately, this situation has begun to change (Weaver, Pargament, Flannelly, & Oppenheimer, 2006 ), for several good reasons. First, spirituality is a “cultural fact” (cf. Shafranske & Malony, 1996 ): the vast majority of Americans believe in God (90%), engage in prayer (90%), and feel that religion is very important or fairly important to them (84%) (Gallup, 2004 ; Poloma & Gallup, 1991 ). Second, as we will see, empirical studies have linked spirituality to a number of aspects of human functioning. Finally, in a more practical vein, the American Psychological Association has defined religiousness as a “cultural diversity” variable. Although it has received relatively less attention than other diversity variables, psychologists are no less ethically obligated to attend to this dimension and reduce potential biases in their professional work with clients of diverse religious backgrounds (see Principle D, Ethical Principles of Psychologists and Code of Conduct of APA, 1992).