Immunoglobulin therapy is a key element in the management of most patients with primary immunodeficiency disease. Allergist/immunologists should be familiar with the appropriate evaluation of candidates for immunoglobulin, the characteristics of immunoglobulin products, and how to use them to provide the best care to their patients. Available immunoglobulin products appear to be equally efficacious, but they are not interchangeable. Minimizing the risk of serious adverse events and controlling minor side effects is important to ideal patient care. Immunoglobulin may be administered intravenously or subcutaneously. Individualizing the choice of immunoglobulin product, mode of administration, and site of care can optimize the clinical outcome and minimize the burden of care. (C) 2016 American Academy of Allergy, Asthma & Immunology.