The following triennial report on the progress in the physics of comets is written in a slightly different form from that in the previous volume of Reports on Astronomy, 1970. All sections were written by the undersigned on the basis of contributions submitted by L. Biermann, A. H. Delsemme, O. V. Dobrovolskii, B. Donn, G. Herzberg, V. P. Konopleva, Rhea Lust, J. Rahe, V. Riives, E. Roemer, S. K. Vsekhsvyatskii, F. Whipple and K. Wurm. The aim of this Report is not to present a review of all papers published and results obtained in recent three years, and many publications are not mentioned explicitly. The published papers which are reviewed in Astronomy & Astrophysics Abstracts are quoted here by eight digits which mean the A & A volume (first two digits) and the reference number.

A generally accepted assumption that the asteroids and comets are keys to the history of the solar system is obviously the reason why the interest in the physical study of comets has been increasing in recent years.