INTRODUCTION: Sudden unexpected death in epilepsy (SUDEP) is the most frequent cause of premature death in epileptic patients. Most SUDEP events occur at night and frequently go unnoticed; the exact pathophysiological mechanisms of this phenomenon therefore remain undetermined. Nevertheless, most cases of SUDEP are attributed to an infrequent yet extremely severe complication of epileptic seizures. DEVELOPMENT: We conducted a systematic literature search on PubMed. Our review article summarises scientific evidence on the classification, pathophysiological mechanisms, risk factors, biomarkers, and prevention of SUDEP. Likewise, we propose new lines of research and critically analyse findings that are relevant to clinical practice. CONCLUSIONS: Current knowledge suggests that SUDEP is a heterogeneous phenomenon caused by multiple factors. In most cases, however, SUDEP is thought to be due to postictal cardiorespiratory failure triggered by generalised tonic-clonic seizures and ultimately leading to cardiac arrest. The underlying pathophysiological mechanism involves multiple factors, ranging from genetic predisposition to environmental factors. Risk of SUDEP is higher in young adults with uncontrolled generalised tonic-clonic seizures. However, patients apparently at lower risk may also experience SUDEP. Current research focuses on identifying genetic and neuroimaging biomarkers that may help determine which patients are at high risk for SUDEP. Antiepileptic treatment is the only preventive measure proven effective to date. Night-time monitoring together with early resuscitation may reduce the risk of SUDEP.