Purpose of Review <p>Hypereosinophilia is defined as an absolute eosinophil count greater than 1500 cells/mm3. This is a condition often observed in the pediatric population, with benign/self-resolving to life-threatening etiologies. Identifying the cause of hypereosinophilia can be challenging, given its broad associated differential diagnosis and diversity of presentations. This review provides an overview of eosinophil biology and explores causes of hypereosinophilia in children, emphasizing diagnostic and therapeutic challenges, while underscoring the importance of recognizing rare causes including primary hypereosinophilic syndrome (HES).</p> Recent Findings <p>Classification of hypereosinophilic subtypes has evolved, as has understanding of etiologies with advances in modern diagnostic tools. Newer therapeutic options with low side-effect profiles have expanded treatment options in patients with HES.</p> Summary <p>Despite recent improvements in medical management, HES remains a serious medical condition with considerable morbidity and potential mortality. Early identification and appropriate treatment can improve prognosis and reduce the burden of disease in children.</p>