Z39.50 grew out of the Linked Systems Project (LSP), an initiative in the 1980s to standardize searching of the major bibliographic databases of OCLC, the Library of Congress, the Washington (Western) Library Network (WLN), and the Research Libraries Information Network of the Research Libraries Group (RLG). Working in parallel to the LSP initiative was the standardization effort around an information retrieval protocol for library applications under the auspices of NISO. The protocol developed from the LSP moved to NISO and was further developed into the Z39.50 information retrieval standard, approved as a NISO standard in 1988. The Library of Congress was designated the official Maintenance Agency and Registration Authority for the Z39.50 standard. As such, LC provides information pertaining to the development and maintenance of the Z39.50 existing and future versions, as well as on the implementation and use of the Z39.50 protocol. A group called the Z39.50 Implementors’ Group (ZIG) assumed a primary role in ongoing development. In c o n j u n c t i on with the Z39.50 Maintenance Agency, the ZIG developed versions 2 and 3 of the Z39.50 protocol (1992 and 1995 respectively), and NISO used its normal consensus and voting procedures to approve the versions as National Standards. In just over a decade, Z39.50 has progressed through three versions, with each version adding vastly greater functionality and sophistication.

  • Version 1 defined the core services of Z39.50.
  • Version 2 formalized the structure of information to be exchanged based on the ISO standard data description language and encoding rules  known as ASN.1 and BER. With consensus on Z39.50 version 2, vendors began to create applications rapidly and momentum grew for compliance with Z39.50 functionality
  • Version 3, the current version of the standard, builds on and includes version 2. Version 3 is extremely powerful in its support for simple to highly complex applications. 

Niso Press (2002). Z39.50 a primer and the protocol. Date of retrieve 1/8/2011.
Retrieve from http://www.niso.org/publications/press/Z3950_primer.pdf