Objective: This article describes a measure developed to assess fidelity of working with the Boston University approach to Psychiatric Rehabilitation (BPR) in Dutch mental health care. The instrument is intended to measure and improve BPR adherence and clinician competence on an individual level and within individual rehabilitation processes. Method: Rotating pairs of 4 BPR specialists used Fidelity of Rehabilitation (FiRe) to evaluate the fidelity of BPR as applied in 114 rehabilitation processes. The content of these processes was documented by the 27 rehabilitation practitioners who delivered the approach. Results: Interrater reliability (.66) was good as were correlations between the first and second assessments (.74), also increasing over time. FiRe was able to distinguish those delivering the approach at an expert level from nonexperts, expressing concurrent validity. FiRe was also related to practitioner attitude toward rehabilitation, a possibly similar construct. In this study, the average level of BPR adherence according to our fidelity model was low. During the 10.5-month review period, overall FiRe scores improved slightly, but this effect was not significant. However, practitioners reported that feedback based on FiRe helped them to enhance their skills. Conclusions and Implications for Practice: This first version of FiRe is a valid and reliable instrument with which to gain insight into the quality and fidelity of individual practitioners’ rehabilitation practices. The instrument used in this study will be further developed in line with study results. More importantly, FiRe raises questions about the definition of good BPR, a topic that should be explored more extensively in future research.