The availability of IgG preparations that could be administered safely by the intravenous route was finally achieved in the early to mid-1980s. Intravenous immunoglobulin (IVIG) revolutionized the treatment of primary immune deficiency diseases (PIDD) and led to the discovery of the therapeutic value of high-dose IgG in autoimmune and inflammatory diseases not associated with PIDD. Improved therapy has improved outcomes and expectations, and most PIDD patients can lead fully active and productive lives. Administration of IgG by the subcutaneous route is effective and safe and overcomes obstacles to the use of IVIG in some patients. Many patients find administration of subcutaneous IgG at home more convenient than receiving IVIG at the Doctor's office or hospital. The coming years will see increased use of subcutaneous immunoglobulin in PIDD, which will be facilitated by advances leading to higher-concentration IgG products and easier delivery.