Abstract The art and science of assessment in supervision are considered in relation to all the dimensions of the supervisory matrix. Issues relating to assessing the patient and the supervisee are considered along with the interactive dynamics between patient and supervisee and supervisee and supervisor that influence this process. The paper considers criteria that the supervisee can utilize in relation to the assessment of the patient and the supervisee and includes issues relating to supervisee development. The complex process of assessment in supervision is also considered in relation to the many interactive layers and conscious and unconscious processes inherent within supervision.