Explores the methods used to identify, measure, and assess the behaviors of individuals using applied behavior analysis (ABA), including behaviors targeted for increase and decrease. In-depth topics include function-based assessment and treatment in behavior analysis; design and details of the assessment process, including selection of an appropriate assessment method; and the methodology, results, and recommendations derived from a functional behavior assessment. Explores assessments such as the DIBELS, ABLLS-R, and VB-MAPP, along with widely used instruments. The capacity to effectively analyze behavior and develop appropriate intervention strategies to bring about behavioral change is a fundamental competency for professionals.