This volume consists of papers presented at the XIII Rolf Nevanlinna — Colloquium held at the University of Joensuu, August 10—13, 1987, The program of the Colloquium concentrated on complex analysis. A substantial part of the program was devoted to the scientific work of Professor Lars V. Ahlfors to celebrate his 80 birthday. This volume is dedicated to Lars Ahlfors, by the consent with all authors.