This chapter examines some of the most important of these theories ranging from Carl Jung’s spiritual account to conflict theories to learning theories to Robert Cloninger’s neurochemical tridimensional personality theory to stages-of-change theories. Complex, sometimes competing, sometimes complementary, this array of primarily psychological theory is fascinating. It also has profound clinical implications. As you read, think about ways, if it is possible, to integrate the various theories and consider how you might apply them to clinical work.