This paper describes the interlending system in the Netherlands and examines the country's union catalogs, the main instrument in the interlending procedure. An overview of the integrated interlending system is provided; the union catalogs of the Royal Library in The Hague, the Technical University Library at Delft, and the library of the Agricultural University at Wageningen are described; and the establishment of the NCC/IBL (Nederlandse Centrale Catalogus van Boeken, Periodieken en Congressen/Interbibliothecair leenverkeer) online union catalog system is discussed. In addition, a description of the development of online library automation in the Netherlands includes the establishment and growth of the library consortium PICA (Project for Integrated Catalogue Automation), the adoption of the Canadian database management system Minisis by the library of the Agricultural University at Wageningen, and the development of PICA "process-systems" for local library use. Finally, the development of the NCC/IBL system is traced from the establishment of a miniformat for titles and the development of software through the current operation of the system, including procedures for loan requests, the implementation of the system for periodicals, and plans for the implementation of the system for monographs. A seven-item bibliography is provided. (KM)