Social work supervision has been an integral aspect of practice since the early 1900s. It assists in maintaining professional identity by that quality services are provided, and high standards are upheld. Supervision enables supervisees to preserve the currency of practice while discerning new skills and knowledge as they navigate the structures in social work practice (Ballantyne et al., 2022). It is also crucial to maintaining critical reflection about professional aspects of the supervisees' role, being accountable, feeling supported and engage in ongoing professional development (Harris, 2020). While much has been written about key aspects of supervision, there remains a paucity in the international literature about the development and use of empirical instruments in social work to support effective outcomes. Some allied health disciplines, such as psychology (Watkins & Milne, 2014), find it commonplace to use supervision instruments to evaluate aspects of supervisory practice; however, this has not occurred in social work. To date, the social work profession has not readily pursued or formalised the practices or processes of effective supervision using evidence-based instruments or more formalised evaluation frameworks. This thesis addresses a significant gap in the social work literature and is crucial in progressing the discourse on supervision capability (Lambie et al., 2018; Swank et al., 2021). It enhances future supervision standards of social work associations in Australia and internationally using elements outlined in the new instrument. Moreover, it is timely for the social work profession. With South Australia achieving registration (Social Workers Registration Act 2021) and the Australian Association of Social Workers (AASW) developing a supervisor credential framework in 2023, supervisors can now articulate how they facilitate aspects of their supervisory practice by drawing on evidence provided in this thesis. Knowing how to provide and receive effective supervision needs to be prominent in social work courses as a result of this research. Fieldwork educators and placement supervisors require better training and an understanding of the capabilities that achieve effective supervision during student placements. While students are required to have their social work practice observed and assessed during placement, there are no mandates for social work supervisors in Australia to assess their level of supervision capability aligned to any standards through formalised instruments (Hicks & Egan, 2023). Therefore, this research calls for the strengthening of supervision capability through supervision standards and all social work courses. This thesis describes findings from two national surveys completed by social work supervisors and supervisees across Australia. In this phase, interviews were also conducted with experienced supervisors across Australia to explore aspects of their supervision practice. Data from the surveys and interviews provided the basis for the second phase, which was to construct capability maps to describe supervision capability. The third phase focused on an initial validation of the newly developed instrument with experienced supervisors through two focus groups. This study resulted in Australia's first evidence-based instrument for social work supervisors to explore their level of capability. Eight domains support effective supervision to ensue through capability. They highlight the ongoing need for continued worldwide research to ensure supervisors can benchmark their supervisory practice through conscientious and judicious use of best evidence (Titler, 2008).