OBJECTIVE:Group-based intervention formats are common in rehabilitation, but no tool for objectively measuring clinical competencies in group facilitation currently exists. We aimed to develop a psychometrically sound group facilitation competency checklist for use in clinical, training, and research settings. METHOD:The Delphi method of expert consensus was used to establish checklist items that clearly describe competencies considered important for effective group facilitation. Inter-rater reliability was determined with two experienced psychologists who used the checklist to rate the competencies of psychology trainees facilitating a memory skills group. RESULTS:After two Delphi rounds, consensus was reached on 17 items, defined as at least 80% agreement among the panel of 15 experts. The four checklist item categories were (a) Facilitating focused group discussion, (b) Communication skills, (c) Interpersonal style, and (d) Session structure. One item was removed after piloting. Inter-rater reliability was excellent (88% agreement) using a simple coding method (competent/incompetent). When using a detailed coding method that discriminated between 'done adequately' and 'done well', inter-rater reliability was weaker (κ = 0.481, 55% agreement); however, it improved to almost perfect after the raters calibrated their standards. CONCLUSION:The new group facilitation competency checklist is fit for purpose for measuring clinical competencies in delivering group-based rehabilitation interventions and can be used in the training of effective group facilitators.