Eosinophilia is defined as elevation of eosinophils in the bloodstream (450–550 cell/μL). There are many reasons for eosinophilia to exist, including parasitic disease, allergic disease, autoimmune, connective tissue disease, rheumatologic disease, primary eosinophilia such as hypereosinophilic syndrome, and as part of a malignant state. Primary care physicians should have an understanding of the variety of diseases or situations that can produce eosinophilia and know in what setting referral to specialty care may be warranted.