Dr. Calhoun graduated from Occidental College in 1960 with a major in philosophy and from San Francisco theological seminary in 1963. After serving two years as a pastor in the United Presbyterian Church USA he entered the University of New Mexico School of Medicine, graduating in 1970. Internship and residency were accomplished at Stanford University. He became a Fellow in dermatology and ministered in a private practice for 12 years. In 1988 he sold his practice to become president of Medical Ambassadors International. During his 17-year tenure at MAI, the Community Health Evangelism model was introduced as the chief operating strategy and the program expanded from 12 to over 80 countries of ministry. After retirement in 2005 he assisted in the founding and guiding of Alliance for Transformational Ministry where he currently serves as Treasurer and Chairman of the Board.