There is increased need for comprehensive, flexible, and evidence-based approaches to measuring the process and outcomes of youth mental health treatment. This paper introduces a special issue dedicated to the Peabody Treatment Progress Battery (PTPB), a battery of measures created to meet this need. The PTPB is an integrated set of brief, reliable, and valid instruments that can be administered efficiently at low cost and can provide systematic feedback for use in treatment planning. It includes eleven measures completed by youth, caregivers, and/or clinicians that assess clinically-relevant constructs such as symptom severity, therapeutic alliance, life satisfaction, motivation for treatment, hope, treatment expectations, caregivers strain, and service satisfaction. This introductory article describes the rationale for the PTPB, its’ development and evaluation, detailing the specific analytic approaches utilized by the different papers in the special issue and a description of the study and sample from which the participants were taken.