This International Standard describes, in the form of a directory, data elements used to support the processes of acquisition, resource description and cataloguing, searching and requesting loan or copy by an end user or an institution. This International Standard includes data elements that are exchanged or are potentially exchanged among bibliographic systems. Those data elements that are not exchanged or not likely to be exchanged are ignored as they do not need standardization. Data elements being handled by transport protocols are not included, only those related to application level protocols. As part of the consolidation phase, the data elements were broadly classed and sub-classed and are presented in two sequences, one by class and sub-class and the other by an alphabetical sequence. The alphabetical sequence includes examples and synonyms identified during the consolidation phase and those found in related interchange protocols and schemas. As the grouping of data elements may differ among different protocols and record schemas, the data elements have been broadly classed and grouped, but no further structure has been made. Similarly, the sequence of data elements, whether or not a data element is mandatory or how it is structured and validated may vary according to its employment and consequently these data element attributes are outside the scope of this International Standard. As new ways of inter-operating evolve, some new data elements may evolve, but the biggest change is usually in the way that existing data elements are grouped. For example, whether a purchase transaction is carried out manually or electronically, the base data elements of the transaction, requester, supplier and object of purchase remain constant, and this is reflected in the fact that most data elements in this International Standard originated several decades ago. To accommodate the potential changing grouping of data elements, an attempt has been made to identify common concepts across processes. For example, a new focus on end user delivery is causing diverse delivery options to be grouped together such that purchase, loan and inter-library loan processes are presented as alternatives; therefore, the identification of common concepts in all these processes is necessary for the development of seamless user interfaces.