Assessing program or intervention fidelity/integrity is an important methodological consideration in clinical and educational research. These critical variables influence the degree to which outcomes can be attributed to the program and the success of the transition from research to practice and back again. Research in the Mindfulness-Based Program (MBP) field has been expanding rapidly over the last 20 years, but little attention has been given to how to assess intervention integrity within research and practice settings. The proliferation of different program forms, inconsistency in adhering to published curriculum guides, and variability of training levels and competency of trial teachers all pose grave risks to the sustainable development of the science of MBPs going forward. Three tools for assessing intervention integrity in the MBP field have been developed and researched to assess adherence and/or teaching competence: the Mindfulness-Based Cognitive Therapy-Adherence Scale (MBCT-AS), the Mindfulness-Based Relapse Prevention-Adherence and Competence Scale (MBRP-AC), and the Mindfulness-Based Interventions: Teaching Assessment Criteria (MBI:TAC). Further research is needed on these tools to better define their inter-rater reliability and their ability to measure elements of teaching competence that are important for participant outcomes. Research going forward needs to include systematic and consistent methods for demonstrating and verifying that the MBP was delivered as intended, both to ensure the rigor of individual studies and to enable different studies of the same MBP to be fairly and validly compared with each other. The critical variable of the teaching also needs direct investigation in future research. We recommend the use of the “Template for Intervention Description and Replication” (TIDieR) guidelines for addressing and reporting on intervention integrity during the various phases of the conduct of research and provide specific suggestions about how to implement these guidelines when reporting studies of mindfulness-based programs