The Mindfulness-Based Cognitive Therapy Self-Assessment Scale (MBCT-SAS) is intended to promote treatment fidelity for trainers and clinicians implementing MBCT groups. It was developed in partnership with clinicians with expertise from a range of disciplines in the delivery of MBCT programs. Unlike similar scales, the MBCT-SAS does not require external assessors and focuses instead upon internal self-mastery of MBCT implementation. The tool assists in assessing adherence to delivery of the MBCT program themes and individual sessions, and appropriateness of themes and content. The scale can be used by individuals to assess their own performance or to complement mentoring and supervision activities. The scale has thus far been used in a limited number of settings, but its cost-effective and accessible format renders it a valuable addition to the fidelity tool spectrum.