The Power Reactor Information System (PRIS) is a comprehensive data source on nuclear power plants (NPPs) in the world. It includes specification and performance history data of operating reactors as well as of reactors under construction or being decommissioned. The NPP design characteristics represent a fundamental part of the PRIS database. They provide important information on the main systems and components and can provide a comprehensive picture of unit design, technology and system configuration. The characteristics can also be used as basic criteria to group reactors with similar or identical design features for operational performance analysis. The aim of this publication is to provide guidelines for PRIS data providers and to detail information about PRIS design characteristics for those using PRIS data for performance analysis, benchmarking or just as a reliable source of technical information related to NPPs.