The search for signals from extraterrestrial civilizations is one of the most intriguing problems raised by modern science. What are these signals, where and how are we to look for them, and should we devote time and effort to this search? These questions were originally in the domain of science fiction, and it is only recently that they began to be considered seriously by astronomers, physicists, biologists, linguists, and philosophers in scientific conferences and in various articles and books. However, despite the numerous questions raised and the various hypotheses advanced, there has been very little real scientific research in this direction. Even the cardinal question of the actual outcome of the encounter of mankind with extraterres­ trial civilization —whether it will be beneficial or harmful —has not been answered unanimously. It suffices to mention how the excessively optimistic prospects of interstellar communication drawn by I. A. Efremov in his’Andromeda Nebula”contrast with the distressing picture envisaged byF. Hoyle and Ch. Elliott in their "A for Andromeda. ” Incidentally, both these books were written by eminent scientists, fully conversant with the grave implications of the problem, and not by professional science-fiction writers who sometimes stand accused of flippant treatment of the subject.The collection looks at various aspects of possible communication with extraterrestrial civilizations.