Immunoglobulin (Ig) therapy is an important method of treatment for a number of immunological, hematological, neurological and dermatological disorders. Over the years, the range of indications in which Ig therapy, either replacement or immunomodulatory, is effective has substantially increased. Although Ig therapy was originally limited to intramuscular injection, intravenous infusion has became the most frequent route of administration, followed by subcutaneous injection. This article presents current information on indications, mechanisms of action, efficacy and practical aspects of intravenous and subcutaneous Ig replacement/immunomodulatory therapy as well as associated adverse reactions.