One of the main current trends in the socio-economic development of society is the informatization of all areas of human activity. The tool for implementing this comprehensive process is information systems (IS) — systems for collecting, storing, processing, converting, transmitting and updating information. The article is devoted to the description of conceptual model of Information System. The model has to describe which entities can be represented at the IS, set the rules and relations (links) between entities. In particular it assumes the entity classification, abstraction, generalization. The purpose of Information Systems is to provide the end-user with necessary information. Depending on specific application area, the information systems may vary greatly in their functions, architecture and implementation. There is, however, one property, which is common to all IS. Any information system is intended for the collection, organization, storage and processing the information. The work is devoted to the problems of description and creation of information models of the IS intensively developing class — digital libraries (DL).