This publication explains how a reactor technology assessment is performed and how the process and its results enable decision making for nuclear power planning and implementation at each of its phases. The methodology has been revised to incorporate developments since the first edition in 2013 and includes feedback from comprehensive training workshops offered for the last six years to Member States introducing nuclear power programmes. The aim of this publication is to help newcomer Member States to understand the complexity involved in the selection of the most suitable reactor technology as well as obligations and responsibilities integral to an unbiased assessment. The publication can also be used by countries that already have nuclear power programmes, to assist in their selection of the next nuclear power plant.