Thevolumecomprises?nalversionsofthepaperspresentedatthe5thInternat- nal Andrei Ershov Memorial Conference "Perspectives of System Informatics," Akademgorodok (Novosibirsk, Russia), July 9-12, 2003. The main goal of the conference was to give an overview of research directions that are decisive for growth in the major areas of research activities in system informatics. The conference was held to honor the 70th anniversary of Ershov's closest colleague, the late Prof. Igor Pottosin (1933-2001), and his outstanding cont- bution towards advancing informatics. The ?rst four Andrei Ershov conferences were held in May 1991, June 1996, July 1999, and July 2001, and they proved to be signi?cant international events. Andrei Ershov was one of the early Russian pioneers in the ?eld of theo- tical and systems programming, a founder of the Siberian School of Computer Science. His closest colleague, Igor Pottosin, worked for the Siberian Branch of the Russian Academy of Sciences from 1958, step by step ?lling positions from junior researcher to director of the A.P. Ershov Institute of Informatics - stems. In later years he headed the Laboratory of Systems Programming in this institute and the Department of Programming at Novosibirsk State University.