This volume contains the proceedings of a symposium held in St. Vincent, Italy, on August 3-6,1976, entitled "Vigilance II: Relationships Among Theory, Physiological Correlates, and Opera- tional Performance." The symposium was sponsored jointly by the Human Factors Panel of the Scientific Affairs Division of NATO and by the Physiology Programs Office of the U.S. Office of Naval Research (Contract N00014-76-C-0722). These sponsorships, and the helpful assistance of Dr. Donald P. Woodward and Dr. John A. Nagay, are gratefully acknowledged. Following the editor's introduction, the papers appear...