Improvement of information technologies inevitably leads to serious transformations of traditional bibliographic resources. These innovations have fully affected the organization and use of network Union catalogues (UC), the qualitative changes in which have been insufficiently studied and covered in professional publications. The article discusses the possibilities of network UC as a tool for information retrieval. The author compares printed and electronic UC, identifies the features and search potential of each of these forms; summarizes the research conducted in the Scientific Research Department of Bibliography of the Russian State Library (RSL) in the framework of RTD project “Information and bibliographic activity of the libraries in the electronic environment”. The author concludes that network UC as a tool of information retrieval have advantages over printed and local electronic catalogues, because electronic catalogues provide free access to the information placed in them from anywhere in the world. Many network catalogues provide the possibility of their independent use as a search tool, even by untrained users due to the accessible interface of the site, clear navigation and clear instructions. Basing on monitoring data of network UC, the author analyses the obstacles for wide use of network UC in information and bibliographic search, and concludes that for effective search it is required a clear and understandable navigation system on the sites with the provision of broad information on the presence of UC and the ways to search them. The article highlights the necessity to promote the capabilities of network UC and other services, including access to the sources reflected in the catalogues.