Preface: Viktor V. Sobolev and His Scientific Legacy.

The study of radiation processes in celestial objects is a fundamental problem in astrophysics. A powerful tool for the solution of this problem is provided by the theory of radiative transfer. One of the founding fathers of modern radiative transfer theory was the prominent full member of the Russian (formerly Soviet) Academy of Sciences Viktor Viktorovich Sobolev.Academician Sobolev was born on 2 September 1915. All his professional life was associated with the Saint Petersburg (formerly Leningrad) State University. From 1948 to 1988 he was the head of the Chair of Astrophysics. He passed away on 7 January 1999 at the age of 83.