A product of the UNISIST International Centre for Bibliographic Descriptions (UNIBIB), this reference manual presents a standardized communication format for the exchange of machine-readable bibliographic information between bibliographic databases or other types of bibliographic information services, including libraries. The manual is produced in loose-leaf format to facilitate updating. Its first section defines in broad outline the format and content of bibliographic records, the concepts of type of bibliographic entity and bibliographic level, and the sets of data elements regarded as essential or optional for the description of each type of bibliographic entity. Names and detailed definitions of each data element are given in the second part, as well as guidance on how the data element content is to be selected and entered onto the machine-readable medium. The third section provides detailed specifications of the carrier format or record structure, character sets and coding, transliteration, physical standards for magnetic tapes, and other aspects primarily of concern to computer system designers. A set of examples with complete bibliographic descriptions follows, and the final section--which is new--presents general guidelines for the production of documentation on individual implementations of the reference manual. Additional background information is given in six appendices. A 36-item bibliography which includes relevant international standards and 10 tables are also provided. (Author/ESR)