Data collection for the standardization phase of the Conners Adult ADHD Rating Scales 2nd Edition (CAARS™ 2) took place from February 2017 to October 2019¹. During the data collection process, participants from all 50 U.S. states and 10 Canadian provinces were recruited, and more than 4,500 CAARS 2 forms were completed. These data were collected for the purpose of developing the CAARS 2 Normative and ADHD Reference Samples, as well as exploring the reliability, validity, and fairness of the scores (see appendix J for demographic characteristics of the samples used in these additional studies). This chapter describes the process by which the CAARS 2 assessment was standardized. Descriptions of the Normative and ADHD Reference Samples are provided, followed by a description of how the CAARS 2 scores were calculated and standardized.