To address the need for new diagnostic criteria, a panel of 101 international experts consisting of neurologists, ophthalmologists, neuro-ophthalmologists, and neuroradiologists convened electronically between April 20, 2018, and March 31, 2021. They used a validated Delphi process-based approach to develop criteria for diagnosis and classification of optic neuritis. Their diagnostic criteria and classification is the topic of the paper about “Diagnosis and classification of optic neuritis” that was published in The Lancet Neurology. Several ERN-EYE members are co-authors.