The OQ®-45.2 feedback system was the first scientifically validated, structured program for conducting routine outcome monitoring in both inpatient and outpatient psychotherapy. In this chapter, we present a brief history of the development of the OQ-45 and its associated measures and feedback system (OQ® Analyst). We also present the empirical evidence supporting the use of OQ® Analyst in routine practice, where a small positive effect is found among full samples, and a larger effect is found for individuals who are predicted to deteriorate in therapy. We present a case example demonstrating the practical utility of the measure and also present the weaknesses and strengths of the system. We conclude that, in an era of multiplying therapeutic theories, techniques, and strategies, OQ® Analyst represents one of the simplest and most effective tools available to broadly improve psychotherapy outcomes.