Certain migraines are labeled as refractory, but the entity lacks a well-accepted operational definition. This article summarizes the results of a survey sent to American Headache Society members to evaluate interest in a definition for RM and what were considered necessary criteria. Review of the literature, collaborative discussions and results of the survey contributed to the proposed definition for RM. We also comment on our considerations in formulating the criteria and any issues in making the criteria operational. For the proposed definition for RM and refractory chronic migraine, patients must meet the International Classification of Headache Disorders, Second Edition criteria for migraine or chronic migraine, respectively. Headaches need to cause significant interference with function or quality of life despite modification of triggers, lifestyle factors, and adequate trials of acute and preventive medicines with established efficacy. The definition requires that patients fail adequate trials of preventive medicines, alone or in combination, from at least 2 of 4 drug classes including: beta-blockers, anticonvulsants, tricyclics, and calcium channel blockers. Patients must also fail adequate trials of abortive medicines, including both a triptan and dihydroergotamine (DHE) intranasal or injectable formulation and either nonsteroidal anti-inflammatory drugs (NSAIDs) or combination analgesic, unless contraindicated. An adequate trial is defined as a period of time during which an appropriate dose of medication is administered, typically at least 2 months at optimal or maximum-tolerated dose, unless terminated early due to adverse effects. The definition also employs modifiers for the presence or absence of medication overuse, and with or without significant disability.