The patent documentation system of the USSR comprise collections at four levels: the very comprehensive collections of the All-Union Patent-Technical Library (VPTB); industry branch oriented files; regional files; and local files of organization and factories. The files of VPTB form the basis for producing abstracts in Russian of foreign inventions, for microfilming industrial designs and utility models of several countries and for issuing various reference and information retrieval publications. The other three categories of files serve, as their names suggest, the needs of specific branches or organizations or are all-purpose files serving a whole region. The system of patent files is continuously upgraded as regards its functions and the services offered. The philosophy governing this as well as techniques for selecting patent documents to be required are described in the article. As in many other countries, there are no libraries in the USSR which exclusively collect files of patent documents (with the exception of the libraries of patent and invention offices). Until recently the All-Union Patent-Technical Library (VPTB) has been practically the sole establishment of this kind. In the early sixties, however, the facilities and collections of VPTB proved to be insufficient to satisfy the public requirements for patent documentation, rapidly growing in this country. This period was marked by efforts directed towards the creation of regional and sectorial files ofm patent documents for the specialists in industry and science. When these files were created the nature, purpose and peculiar features of industrial property documents was fully taken into account. At the same time, important decisions were taken, concerning the setting up of the State system of patent documentation files, the problems of controlling the process of forming the files became highly important. In the system of patent documentation being established, the industry branch oriented and regional files collected within the central bodies of scientific and technical information (STI) have become the major components. They provide facilities for conducting thorough patent searches to specialists of the industrial ministries and organizations of the country, irrespective of where the enterprise or organization is located. At the present stage, the structural arrangement of the patent documentation system is represented by collections at four levels: The first or higher level — VPTB. The collections here comprehensively represent the files of domestic and foreign patent documents over an unlimited period of time. The second level — industry branch oriented files; they cover exhaustively their respective industry sectors, mainly backlogged over the period of renewal of industrial products; they are primarily represented by patent documents of the countries where the industry sector of interest is highly developed. The third level — regional files, of all-purpose character. They are compiled of patent documentation of the major industrially or economically developed nations and offer facilities for conducting various comprehensive patent-related studies, including patent clearance searches. The fourth level — local files of organizations and factories compiled according to their specific needs; the period, fields and countries covered — all this is determined in accordance with the general layout of the respective branch-oriented file; local files are thus the source of specialized scientific and technical information of the organization or factory concerned.