Many pediatric diseases demonstrate blood or tissue eosinophilia. Included among these disorders are common atopic diatheses such as asthma as well as the rarer conditions of hypereosinophilic syndrome and eosinophilic gastrointestinal disorders. Eosinophil trafficking and activation in target organs leads to tissue damage and ongoing reparative attempts that can ultimately result in changes in organ structure and function. Recent treatment with biologic agents such as tyrosine kinase inhibitors and anti-interleukin-5 has offered new therapeutic options in certain eosinophilic disorders. Eosinophilic disorders such as eosinophilic esophagitis are increasingly being diagnosed in children, but many lessons in disease pathogenesis, diagnosis, optimal treatment, and natural history continue to be learned.