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‘Query encephalitis’ is one of the most common reasons for inpatient neurology referral in the context of an acutely confused patient. Growing evidence suggests that time to treatment is a key determinant of outcome in both infectious and autoimmune encephalitis; hence, these two causes should be considered simultaneously at presentation. However, under-recognition and the existence of several mimics make a rapid diagnosis of encephalitis challenging. Appreciation of clinical syndromes can guide aetiological investigation and consequent treatment. In this article, we discuss clinical phenotypes associated with both infectious and autoimmune encephalitis, as well as a systematic approach to their investigation and up-to-date treatment strategies. We also highlight ongoing areas of research, such as metagenomics and therapeutic trials.