Abstract: The presentation of eosinophilic esophagitis (EoE) is heterogeneous with varied clinical, endoscopic, and histologic features impacting the severity of the condition. Until recently, however, and in contrast with many other conditions, there has been no standardized way to measure disease severity in EoE. A clinically applicable method for assessing severity in routine practice has been recognized as necessary to standardize assessment and management of EoE. Therefore, the American Gastroenterological Association has sponsored a consensus conference to determine elements of severity in EoE and develop the first tool to measure severity. This article presents details of this severity metric, which is known as the Index of Severity in EoE (I-SEE), and outlines the elements within I-SEE and how to categorize EoE as mild, moderate, severe, or inactive. The domains of I-SEE include symptoms and complications, inflammatory features (both endoscopic and histologic), and fibrostenotic features (both endoscopic and histologic). The article also provides an update on emerging data related to I-SEE and discusses the future studies necessary to implement I-SEE as part of a treatment framework in EoE.