Abstract. In the last decade, the Nuclear Energy Agency (NEA) of the OECD co-ordinated an international initiative to develop understanding and guidelines related to the longer-term preservation of records, knowledge and memory (RK&M) regarding radioactive waste repositories, the so-called “RK&M Initiative”. Their final report (NEA, 2019) can be read as a general guide to the RK&M preservation topic. In terms of practical support, the group prepared an RK&M preservation toolbox, comprising 35 different preservation mechanisms. Amongst those are classical, much discussed tools such as “archives”, “surface markers” or “land use control”, hitherto less discussed tools such as “international regulations”, “small time capsules” or “clear and planned responsibilities”, and two entirely new concepts: the Set of Essential Records (SER) and the Key Information File (KIF). In the current contribution, I present these two concepts, pointing out their role both in the wider RK&M preservation context (i.e. in the toolbox as a whole) and in the narrower “documents” context. My main focus is a comparative approach, addressing the peculiarities of the KIF and the SER concepts by working out the differences between the two. It becomes apparent that the KIF is far from being a condensation of the SER, but in fact KIF and SER are independent concepts: in terms of their authors/creators, their target audiences, and first and foremost their functioning, i.e. “how” they contribute to RK&M preservation.