The human factors engineering (HFE) validation of a nuclear power plant control room design, or of a design modification (e.g., for modernization), is a complex undertaking that faces many technical and logistical challenges. These challenges include conducting validations that address the diversity of operating conditions, staffing configurations, and failure scenarios that the plant will experience, or must be designed to tolerate. Such challenges must be addressed within the practical constraints of available resources (e.g., test personnel, participants, testbeds, and time). How these challenges are addressed can impact the confidence that vendors, nuclear plant operating companies, and regulatory authorities have in validation results and conclusions. Since 2013, the Nuclear Energy Agency’s Working Group on Human and Organizational Factors has been working with industry experts in control room validation to identify and advance the development of methods for enhancing confidence in control room validations. The most recent product of these efforts is a working group report that describes a general approach and rationale for validating systems through a series of successive, coordinated validation activities. The working group refers to this approach as, multi-stage validation (MSV). This paper summarizes the central concepts and issues discussed in the working group report, including the defining characteristics of MSV and those that characterize an effective MSV implementation. Also addressed in this paper are methods and issues important to MSV implementation and its further development as an approach to the HFE validation of nuclear power plant control room designs and modifications.