Data collection for the standardization phase of the Conners 4th Edition (Conners 4®) took place from May 2019 to March 2020. During the data collection process, participants from all 50 U.S. states and all 10 Canadian provinces were recruited, and more than 9,500 Conners 4 forms were completed. These data were collected for the purpose of developing the Conners 4 Normative and ADHD Reference Samples and scores, as well as exploring the reliability, validity, and fairness of the scores (see appendix F for demographic characteristics of the samples used in these additional studies). This chapter describes the process by which the Conners 4 assessment was standardized. Descriptions of the Normative and ADHD Reference Samples are provided, followed by a description of how the scores were calculated and standardized.