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. This report proposes and describes the concept of a Set of Essential Records (SER) as an important component of a RK&M preservation strategy. The SER is designed to be a compilation of actual records, selected because they would be required for future generations to understand the repository system and its performance, and to assist them in making informed decisions. The guidance set forward in this document is complemented by appendices, illustrating an example procedure for the selection of records to form part of the SER.