This volume contains the proceedings of the First All-Union Conference on Extra­ terrestrial Civilizations and Interstellar Communication, held at the Byurakan Astrophysical Observatory of the Armenian Academy of Sciences in May 1964.The basic premise of the conference was the multiplicity of inhabited worlds.In the light of this assumption, the participants discussed the possibility of existenceof alien civilizations at various levels of development and considered the means for establishing interstellar communications. It was agreed that the best course would be to start simultaneous reception and transmission of radio signals. Artificiality criteria differentiating the multitude of natural radio signals received by radio-astronomic equipment from space from artificial radio signals sent by technically advanced alien civilizations were discussed in considerable detail. The problems of cosmic linguistics were also touched upon at the conference.