The present volume contains the invited lectures given at the Symposium on Integrable Quantum Field Theory, organised by the Research Institute for Theoretical Physics of the University of Helsinki in Tvarminne, Finland, 23-27 March, 1981.
We are grateful to Dr. E.K. Sklyan[n, who, although unable to attend due to a last-minute delay, agreed to submit together with Dr. P.P. Kulish an expanded review of the work done by the Leningrad school.