This volume comprises the papers presented at the Third International Andrei Ershov Memorial Conference Perspectives of System Informatics", Akadem- rodok (Novosibirsk, Russia), July 6{9, 1999. The main goal of the conference was to give an overview of research directions which are decisive for the growth of major areas of research activities in system informatics. The conference was the third one in the line. The r st and second inter- tionalconferencesPerspectivesofSystemInformatics"wereheldinNovosibirsk, Akademgorodok, in May, 1991, and June, 1996, respectively. Both conferences gathered a wide spectrum of specialists and were undoubtedly very successful. The third conferenceincluded many of the subjects of the second conference, such as theoretical computer science, programming methodology, new infor- tiontechnologies,andthepromising eldofarti cialintelligence|asimportant components of system informatics. The style of the second conference was p- served to a certain extent in that there were a considerable number of invited papers in addition to the contributed papers. However,posters were replaced by short talks mainly given by young researchers.