This activity is now closed. The information on this page is provided for historical purposes only.

This term refers to two information standards:

  • the International Standard, ISO 23950: "Information Retrieval (Z39.50): Application Service Definition and Protocol Specification"
  • the American standard, ANSI/NISO Z39.50.

The Library of Congress is the Maintenance Agency and Registration Authority for both standards, which are essentially the same.

Z39.50 is a computer-to-computer communications protocol designed to support searching and retrieval of information in a distributed network environment.

The Z39.50 standard continues to evolve to meet the changing needs of information creators, providers, and users.


The goal of this work is twofold:

  • to continue the advancement of the standard
  • to provide consultation on the standard to OCLC and the LIS community.

Why OCLC is conducting this research and how it helps libraries

  • Z39.50 provides the database searching infrastructure for all our products
  • Z39.50 supports the discovery and exchange of MARC-21 records between library systems
  • Z39.50 is one of the protocols used to search digital repositories


Research team

We are a worldwide library cooperative, owned, governed and sustained by members since 1967. Our public purpose is a statement of commitment to each other—that we will work together to improve access to the information held in libraries around the globe, and find ways to reduce costs for libraries through collaboration.