This paper is the first to present a model for mentalization-based supervision of professionals working with environmental therapy. Mentalization-based supervision should be based on a mentalizing stance and theory aligned with the current mentalizing perspective, that is, the theory of attachment, mentalization and should aim at establishing ‘we-mode’ and epistemic trust. This paper offers a practical guide, models, and templates that are easy to apply and beneficial for the supervisor to underpin the mentalizing stance and focus on mentalizing processes during complex supervision sessions with groups of supervisees. The approach and method of supervision are demonstrated through a clinical case, and the supervision process is illustrated via templates to aid the reader who is a supervisor for groups in this field. The article is based on current theory and research on mentalization and on the clinical practice of supervision in psychiatric inpatient treatment and residential care.