Measurement-based care (MBC) is the routine collection of data using standardized, validated measures and use of these data to guide treatment. MBC has been implemented throughout medicine to improve patient outcomes, but its use in mental health care remains low. This article summarizes the evidence of MBC’s efficacy in adults then reviews the sparser data in youth mental health care. The literature indicates that MBC must be administered immediately before or during every encounter, results must be available to and reviewed by providers immediately, results must be shared with the patient, and results must be used to guide treatment.