Despite the high reported prevalence and burden of cognitive dysfunction in systemic lupus erythematosus (SLE), there is poor understanding of its aetiology, clinical assessment, and management. In part, this lack of understanding is due to conceptual disorganisation in the available literature. In this Review, we address key knowledge gaps in the nomenclature, assessment, and interpretation of cognitive dysfunction in SLE. We apply basic principles of neuropsychology and incorporate lessons from other disease states to recommend principles that can help researchers to design studies in SLE. Better understanding of the trajectory of cognitive dysfunction in SLE will help to inform therapeutic trials, including the appropriate selection of outcome measures to capture clinically meaningful responses.