Reliability of electric power systems remains an important societal issue. While transmission disturbances draw national attention and scrutiny, service interruptions at the distribution level are the primary concern of the end-use customer and their regulatory and governmental representatives. Much effort has been expended in developing methods to uniformly and consistently quantify the reliability of distribution service based on electric system performance. However, the results of a nationwide survey of recorded information used for calculating distribution reliability indices performed in 1998 by the Working Group on System Design (Now Distribution Reliability) indicate that significant inconsistencies exist in the data, categorization of that data, and in the collection processes used within the industry. This guide discusses the collection; categorization and usages of information related to electric power distribution interruption events and will be used in the development of industry guidelines. This guide presents a minimal set of data and a consistent categorization structure that when used in combination with IEEE Std. 1366TM will promote consistency in how the industry collects data for the purpose of benchmarking distribution system performance.