As part of the INPRO methodology this manual provides guidance on assessing a nuclear energy system in the area of economics. This is an independent assessment of the economic competitiveness of nuclear power, compared with available alternatives. The publication starts with a short description of the goals and output of an energy system planning study, followed by general background information on performing an INPRO economic assessment and presents a discussion of the basic principle, the associated user requirements and criteria. In the appendices I-IV, additional background information on economic terms and support tools is provided.