Psychologist and philosopher William James (brother of Henry) is regarded by most psychologists of religion as the founder of the field. He was president of the American Psychological Association and wrote one of the first psychology textbooks. In the psychology of religion, James' influence endures to this day.
The Varieties of Religious Experience is considered to be the classic work in the field. To quote Wikipedia, "James was most interested in understanding personal religious experience. The importance of James to the psychology of religion - and to psychology more generally - is difficult to overstate. He discussed many essential issues that remain of vital concern today. What makes James writing so special is that he could take a very complex subject and, without watering it down, make it understandable to 'the rest of us.'"
This is a must listen for anyone interested in religon and man's search for the spritual. It is written for laymen, thus easy to understand, but remains penetrating and brilliant.
"Believers and unbelievers (and semi-believers) will continue to find in it both a resource and a challenge. Quaint though some of it may seem at first in language and approach, The Varities of Religious Experience, can itself become for the contemporary reader not only an intellectual exercise but a religious experience." (Jaroslav Jan Pelikan, Sterling Professor of History Emeritus, Yale University)