In pursuing assessment excellence, clinician-educators who design and implement assessment are pivotal. The influence of their assessment practice in university-run licensure exams on student learning has direct implications for future patient care. While teaching practice has been shown to parallel conceptions of teaching, we know too little about conceptions of assessment in medical education to know if this is the case for assessment practice and conceptions of assessment. To explore clinician-educators' conceptions of assessment, a phenomenographic study was undertaken. Phenomenography explores conceptions, the qualitatively different ways of understanding a phenomenon. Data analysis identifies a range of hierarchically inclusive categories of understanding, from simple to more complex, and the dimensions that distinguish each category or conception. Thirty-one clerkship convenors in three diverse Southern settings were interviewed in three cycles of iterative data collection and analysis. Four conceptions of assessment were identified: passive operator, awakening enquirer, active owner and scholarly assessor. Six dimensions were elucidated to describe and distinguish each conception: purpose of assessment; temporal perspective; role and responsibility; accountability; reflexivity and emotional valence. Additionally, three characteristics that appeared to track the progressive nature of the conceptions were identified: professional identity, assessment literacy and self-efficacy. These conceptions encompass and extend previously described conceptions across different educational levels, disciplines and contexts, suggesting applicability to other settings. There is some evidence of a relationship between conceptions and practice, suggesting, together with the hierarchical nature of these conceptions, that targeting conceptions during faculty development may be an effective approach to enhance assessment practice.