Conners-3 rating scale is primarily used in the assessment of ADHD and it has been found to be instrumental in variety of areas such as screening, assessment, and treatment monitoring. Most, if not all, rating scales are developed on western standards and available in different languages especially, English. For this reason, we adapted the Conners-3 teacher and parent rating scales since we are ethically responsible to have a rating scale that assess ADHD and takes into consideration the linguistic and cultural differences among the Lebanese population. Conners-3 aims to measure ADHD and most common comorbid problems in children and adolescents. The purpose of this study was to adapt and validate the Conners-3 teacher and parent rating scales to the Lebanese context. The International Test Commission (ITC) guidelines were used for translating the rating scales, and then they were reviewed by professionals, piloted, revised, and then administered. The sample consisted of students enrolled in grades 1 through 12 from nine schools. Their parents (455) and 108 teachers of (509) students filled the respective Conners-3 rating scales. The reliability and validity of the scales was investigated by examining the internal consistency and test-retest reliabilities, construct validity in terms of gender and age differences, discriminant validity between ADHD and non-ADHD groups, and Exploratory Factor Analysis. The reliability coefficients and discriminant validity were moderate to high. Age and gender differences were not well defined, and the obtained factor structure partially resembled that of the original Conners-3. Norms in terms of T scores and percentiles were reported. Results were discussed and limitations and recommendations for the future studies were proposed.