This is the final full report of the 4-year international project on Reversibility and Retrievability (R&R) launched in 2007 by the OECD/NEA Radioactive Waste Management Committee (RWMC). Major milestones in the project have been the conduct of a bibliographic survey, a survey of NEA countries' positions, and discussions within an ever-widening group of interested parties that culminated with an International Conference and Dialogue in Reims, France (December 2010). The report surveys, in an empirical manner, the statements that have been made over the decades about reversibility and retrievability, thereby documenting a history and an evolution across time. It surveys, also empirically, how R&R have been integrated (or not) in national programmes, or in various stakeholders' positions on waste disposal, giving a respectful adn empowering grasp of the different conditions in which R&R may be applied. The report proposes defintions and conclusions that reflect the mutual understanding built up in the R&R working group made up of persons from many nations.