This publication is an update of the guidance given in the area of infrastructure in Volume 3 of IAEA-TECDOC-1575 Rev.1 (2008), Guidance for the Application of an Assessment Methodology for Innovative Nuclear Energy Systems. It is based on recommendations presented by Member States participating in INPRO, IAEA experts and the IAEA INPRO group. The publication provides guidance on assessing a nuclear energy system (NES) in the area of nuclear infrastructure. Within the INPRO methodology, a nuclear infrastructure can be defined as the collection of necessary capabilities of national institutions to achieve long term sustainability of a nuclear power programme. Several aspects are discussed in detail in this publication, in particular the importance of public acceptance of a nuclear power programme and the necessary human resources to establish and operate such a programme. Additionally, INPRO methodology defines measures that a designer and the State should take to reduce the necessary effort to establish and maintain a nuclear infrastructure.