In this in-depth review, presented by Princess Ogbogu, MD, and developed in collaboration with Michael Wechsler, MD, MMSc, the wide-ranging presentations of HES will be reviewed, along with pathophysiology, classification, and acute and chronic management. Learnings from the presentation will be tied together with a case-based presentation of idiopathic HES, allowing learners to see how guideline recommendations and novel clinical trials can be applied in a real clinical setting.