Background: Immunoglobulin replacement therapy (IGRT) is the foundation of treatment for the majority of patients with primary immunodeficiency. Clinical history and laboratory evaluation define the patients for whom IGRT is necessary and appropriate. During the 70 years since the first patient was treated, new products have led to the development of several modes of administration that facilitate the individualization of treatment that enables the optimization of care. Objective: The objective was to explain the assessment of candidates for IGRT and approaches to reevaluating recipients of IGRT to decide on the need to continue treatment and to review the approaches to optimize IGRT. Methods: The relevant literature was reviewed in the context of the author's experience supervising > 20,000 IGRT treatments over a 40-year period. Results: Providing the most appropriate form of IGRT for individual patients ameliorates disease and lessens the burden of care for patients with primary immunodeficiency. Conclusion: IGRT is safe and effective when used to treat patients with primary immunodeficiency who meet established and appropriate clinical and laboratory criteria.