The design and construction new Nuclear Power Plants (NPPs) as well as their modifications need to address Human Factors Engineering (HFE) considerations, coming as a requirement from nuclear regulatory bodies. For new plants in the United States (US), HFE considerations must be addressed as part of Chapter 18 of any plant Safety Analysis Report, following guidance coming from regulatory guide RG 1.206, NUREG-0800 and NUREG-0711 [Ref. 1], the latter with the deepest level of detail for each of the activities described The afore mentioned HFE regulations have been developed for application in the US plants, but many other nuclear regulatory bodies in the world endorse these US Nuclear Regulatory Commission (NRC) regulations, as for now they provide the most detailed guidance in this field, compared to other Nuclear Standards associated to HFE. Element 10 of NUREG-0711 [Ref. 1], addresses the HFE Verification and Validation (V&V) activities with the objective to comprehensively determine that the HFE design conforms to HFE design principles and that it enables plant personnel to successfully perform their tasks for assuring plant safety and operational goals. One of the main activities of this Element is Integrated System Validation, for determining if an integrated system’s design (i.e., hardware, software, and personnel elements) meet plant operation objectives, performance requirements, supporting safe plant operation. This paper shows the experience and lessons learned by Tecnatom in the development of new NPP control rooms and design modifications in existing control rooms, always in relation to HFE, and focusing in multistage Validation approaches. In Tecnatom’s experience, the use of multistage validations is the most effective way to ensure that the final product meets the HFE requirements. The paper will include examples and lessons learned in new design and modification projects completed by Tecnatom. The paper ends summarizing: 1. The benefits obtained from the executions of a multistage validation approach. 2. The need to develop guidance related to this approach. The description of benefits and needs has always the objective of facilitate future execution of projects in new builds or design modifications, where HFE can contribute to obtain the best results, products and designs, from a technical and economical viewpoint.