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