This guide to the selection of a Z39.50 client presents numerous evaluation criteria and poses questions that should be asked when reviewing and testing end-user products. The areas for consideration include whether to buy or build a Z39.50 client, the end-user's requirements, connecting to a remote server, searching, managing the search response, Z39.50 services, the vendor, and testing. As some knowledge of the Z39.50 standard is helpful in the selection process and contributes to an understanding of how a Z39.50 client works, brief descriptions of some of the major aspects of Z39.50 are also included.