External scrutiny of higher education courses is evident globally, but the use of an external examiner from another institution for the purposes of quality assurance has been a distinguishing feature of UK higher education since the 1830s. However, the changing higher education context has led to mounting criticism of the system and the identification of a number of largely unchallenged assumptions underpinning it. One such assumption is that external examiners are assessment literate. This study evaluates levels of assessment literacy demonstrated within the written reports of external examiners. Findings indicate variable levels of assessment literacy and identify aspects of the concept that require attention. Wider questions concerning the conceptualization and future development of the external examining system are considered.