The reliability of the CAARS 2 scales was explored through a variety of studies. First, internal consistency was examined with alpha, omega, and mean inter-item correlations, with all values meeting or exceeding typical guidelines for reliability. Standard error of measurement values were calculated, and results demonstrated the small amount of error in estimated true scores. For practical applications, these values were also provided to facilitate the creation of confidence intervals around the CAARS 2 T-scores. Test information was examined, demonstrating considerable amounts of precision across the target range for CAARS 2 scales for each rater type. Further, studies were conducted to assess the test-retest reliability of the CAARS 2 scores, with results supporting the stability of scores over a 2- to 4-week period. Lastly, inter-rater reliability studies were conducted to compare the scores between different raters. As expected, raters of similar and different types showed modest associations between their scores, supporting the best practice of obtaining multiple perspectives when completing an ADHD evaluation. Overall, the results presented within this chapter provide strong evidence for the reliability of the CAARS 2 scores.