Background: Systemic immunomodulatory treatment is actively recommended in the treatment for moderate to severe atopic dermatitis (AD) patients. However, consensus criteria for the classification of AD severity or treatment refractoriness have not been established yet. Objective: To establish consensus criteria on the definition of severity classification and treatment refractoriness of AD to provide a basis for proper treatment strategy. Methods: The Korean Atopic Dermatitis Association (KADA) comprised a task force team to establish a definition of moderate to severe AD. A draft of definition of moderate to severe AD was made on the basis of evidence. The recommendation was confirmed by KADA members through a web-based survey. Results: KADA approved that AD with 16≤eczema area and severity index (EASI)<23 should be basically defined as moderate AD whereas AD with EASI score ≥23 should be considered as severe AD. They agreed that it would be reasonable to raise the severity level if patient's daytime or nighttime pruritus numerical rating scale is equal to or higher than 7 (≥7) or dermatology life quality index score exceeds 10. AD patients who do not reach EASI 50 after appropriate treatment for three months should be considered as a non-responder. Patients with recurrence (EASI ≥16) within three months after cessation of treatment should be considered as a recurrent AD. Conclusion: KADA built a consensus of definition of moderate and severe AD and treatment-refractoriness. These guidelines are expected to help physicians determine proper treatment options in need. (Ann Dermatol 31(6) 654∼661, 2019