The JISC Information Environment Service Registry (IESR) is a machine-to-machine middleware shared service providing a single central catalogue of quality descriptions of collections of resources available to researchers, learners and teachers in the UK, along with details of the services that provide access to those collections. The collections and services are described according to a set of metadata, which is defined by IESR, but is based on open standards wherever possible. The prototype registry is implemented as an XML repository indexed with the Cheshire II information retrieval software, with an associated metaregistry to support browsing and data capture. Several interfaces for server-toserver retrieval of IESR XML descriptions are available, as well as a Web interface.