Personality Types : Hardback : Houghton Mifflin : 9780395798676 : 0395798671 : 29 Oct 1996 : Don Richard Riso, M.A., is the most widely published and the bestselling author of books on the Enneagram. This is the revised and expanded edition of the classic on understanding the human personality--more than 150,000 copies sold! In addition to updating the descriptions of the nine personality types, this book uncovers the Core Dynamics, or Levels of Development, within each type.