The first part of the study gives a summary of the changes that the library field underwent as a result of the development of information technologies. The overview touches upon the changes in the bibliographical data processing, the national MARC formats supporting data exchange and the efforts to harmonise these formats. The second part of the study focuses on a development project of the LIS Department of Debrecen University. Based on XML language, a markup language was elaborated that makes it possible for librarians to formalise the bibliographic description according to their own special needs. The language is called Bibliographic Description Markup Language (BDML). Its flexibility permits a better exploitation of the possibilities offered by bibliographic description. BDML is based on Hungarian cataloguing standards. Filters and style definitions can easily be applied to BDML.