In the 1970s Don Riso was exposed to the Enneagram personality type material by way of some notes that were being passed around the Jesuit community. In 1975 he left the Jesuits and began developing the material more fully. In 1987, he published one of the first books on the Enneagram personality types. Riso introduced a number of unique ideas to the system such as levels of health or development, directions of integration and disintegration, and many others.
In the early 1990s Russ Hudson joined him in his enneagram work publishing additional books and other material as well as training Enneagram teachers. In 1995 the two founded The Enneagram Institute.