Early 2003 the digital archiving system of the National Library of the Netherlands (KB) was taken into production. This system is called the e-Depot and its technical heart is the IBM system called Digital Information Archiving System (DIAS). The e-Depot is built according to the recommendations in the OAIS reference model and is dedicated to the long-term storage of and access to large quantities of digital publications. To control safe storage and provide for future rendering of the digital documents, extra functionality was needed. Therefore, at the same time the system was taken into production, a joint KB/IBM project group started with the design, development and implementation of the Preservation Manager. This system provides the functionality for defining and managing the technical environment needed to render the electronic resources stored in DIAS. In this paper we present the design of the Preservation Manager, its rationale, and the way it is used within the operational digital archiving environment of the KB e-Depot.