This volume presents work that evolved out of the Third Conference on Situation Theory and Its Applications, held at Oiso, Japan, in November of 1991. The chapters presented in this volume continue the mathematical development of situation theory, including the introduction of a graphical notation; and the applications of situation theory discussed are wide-ranging, including topics in natural language semantics and philosophical logic, and exploring the use of information theory in the social sciences. The research presented in this volume reflects a growing international and interdisciplinary activity of importance for many fields concerned with information.