Ongoing efforts to refine the classification of the epilepsies have been made by the International League Against Epilepsy (ILAE) almost since its inception in 1909 and gained special momentum in the early 1960s when new concepts of classification were proposed by Henri Gastaut.1-3 Intense debate and acquisition of new knowledge in the next two decades led to the landmark 1985 ILAE “Classification of Epilepsies and Epileptic Syndromes,”4 which was soon followed by a revised version ratified by the ILAE General Assembly in 1989.5 The 1989 Classification has been highly influential worldwide and has had a major impact on epilepsy care and research. The work presented herein builds on the efforts of many over more than a century; we acknowledge their seminal contributions in the development of the classification of the epilepsies.

Although many concepts outlined in the 1989 ILAE classification remain valid to this day, it has become increasingly clear that a revision is needed to account for subsequent scientific discoveries that over the last few decades have fundamentally changed our understanding of the epilepsies as well as our approach to the diagnosis and management of individuals with epilepsy.

Epilepsy classification is the key clinical tool in evaluating an individual who is presenting with seizures. It influences every clinical consultation yet its impact stretches far beyond the clinical domain to clinical and basic epilepsy research and to the development of novel therapies. Classification serves many purposes: providing a framework for understanding the type of seizures that the patient has, the other seizure types that are more likely to occur in that individual, the potential triggers for their seizures, and often their prognosis. Classification also informs the risks of comorbidities including learning difficulties, intellectual disability, psychiatric features such as autism spectrum disorder, and mortality risk such as sudden unexpected death in epilepsy (SUDEP). It is notable that classification often guides the selection of antiepileptic therapies.

Classification of the epilepsies has evolved dramatically since its inception in the 1960s.6-9 The many iterations in classification reflect advances in understanding phenotypic patterns and underlying mechanisms, based on major contributions from clinical and basic research from around the world. These insights are incorporated into the many facets of clinical care for patients and lead to progress in the development of innovative treatments, be they pharmacologic or dietary therapies, surgical approaches or device development. Classification will always be a dynamic process, iterative to the new insights gained through research and improved understanding of this heterogeneous group of diseases. Its continued evolution into the future promises to lead to further advances in patient care.

Classification engenders passionate debate. This is partly because it is built on the complex clinical constructs underpinning epilepsy diagnosis and partly because it is so critical to our daily practice. Classification has been based on expert opinion drawing together epileptologists and related experts from around the world. Although there is no doubt that the desired endpoint is a scientifically based classification, our understanding is not sufficiently advanced to construct a classification on a scientifically rigorous basis.9 Thus current proposals are based on a combination of the latest scientific understanding coupled with high‐level expert opinion, including an extensive consultation with epilepsy professionals and the wider epilepsy community worldwide.

When a patient presents with seizures, the clinician works through several critical steps in making a diagnosis. Before attempting to classify a seizure, the physician must determine whether the paroxysmal event is indeed an epileptic seizure with a myriad of differential diagnoses being possible. These include convulsive syncope, parasomnias, movement disorders, and other nonepileptic events (https://www.epilepsydiagnosis.org/epilepsy-imitators.html). This diagnostic step is taken as already established at the point of beginning to classify the patient's epilepsy.

In terms of epilepsy classification, the clinician starts by classifying the type of seizure. This is the subject of the companion paper on the new classification of seizure types.10 Then, the patient's type of epilepsy needs to be classified and, in many cases, a specific epilepsy syndrome diagnosis can be made. Just as importantly, strenuous attempts to identify the etiology of the patient's epilepsy should be made at each step in the diagnostic pathway. Classification of seizure type and epilepsy type both take into account the results of investigations such as electroencephalography (EEG) and neuroimaging studies together with other studies exploring the underlying etiology of the epilepsy. Herein, we present the first major Classification of the Epilepsies since the last ratified ILAE Classification in 1989.