Assessment and feedback research constitutes its own 'silo' amidst the higher education research field. Theory has been cast as an important but absent aspect of higher education research. This may be a particular issue in empirical assessment research which often builds on the conceptualisation of assessment as objective measurement. So, how does theory feature in assessment and feedback research? We conduct a critical review of recent empirical articles (2020, N = 56) to understand how theory is engaged with in this field. We analyse the repertoire of theories and the mechanisms for putting these theories into practice. 21 studies drew explicitly on educational theory. Theories were most commonly used to explain and frame assessment. Critical theories were notably absent, and quantitative studies engaged with theory in a largely instrumental manner. We discuss the findings through the concept of reflexivity, conceptualising engagement with theory as a practice with both benefits and pitfalls. We therefore call for further reflexivity in the field of assessment and feedback research through deeper and interdisciplinary engagement with theories to avoid further siloing of the field.