Radioactive waste repositories are designed to be intrinsically safe in that they are not dependent on the presence or intervention of humans. In response to this challenge, the Nuclear Energy Agency initiated the Preservation of Records, Knowledge and Memory (RK&M) Across Generations Initiative, calling on the international community to help create specific means to preserve RK&M. The concept of a key information file (KIF) emerged in response to the challenge presented by the large volumes of RK&M material generated by national disposal programmes. This concept has been developed into an important component of a RK&M preservation strategy. The KIF is designed to be a single, short document, produced in a standard format, with the aim of allowing society to understand the nature and intent of a repository, and thus to reduce the likelihood of unnecessary human intrusion. It should be made openly available and ultimately be widely distributed. This report describes the KIF concept in detail, in a manner that should enable those concerned with any particular repository to create their own versions. Three draft key information files, currently under development to support RK&M preservation in France, Sweden and the United States, are provided as examples.