The Coordinated Research Project on Probabilistic Safety Assessment Benchmarks for Multiunit Multi Reactor Sites (2018-2022) brought together the experts from the IAEA Member States with mainly water-cooled reactor technologies to utilize, test and further develop their current or planned probabilistic safety assessments methods and assumptions by conducting and comparing results of meaningful multiunit multi reactor type probabilistic safety assessment (MUPSA) benchmark exercises. The objective was to share national expertise and participate in shared benchmark calculations. These calculations involved the development of MUPSA, based on single unit probabilistic safety assessments available in Member States. This publication is intended for nuclear engineers, researchers, code developers, experimentalists in nuclear energy fields, reactor vendors and developers, university professors and students, regulatory experts, and nuclear power plant planners.