Immunoglobulin G4-related disease (IgG4-RD) is a recently described systemic inflammatory disease characterized by increased serum IgG4 concentrations, lymphoplasmacytic infiltrations, storiform fibrosis, and obliterative phlebitis. However, although IgG4-RD has become increasingly recognized, the number of patients with IgG4-RD remains unclear. Data from several studies indicate that patients who have a T-helper type 2 (Th2-) dominant immune response, which leads to the hyperproduction of Th2 cytokines, then progress to IgG4-RD. Glucocorticoids are the most common treatment for IgG4-RD and generally, patients have a good response—a characteristic of IgG4-RD. However, relapses during the tapering of glucocorticoid therapy are common. Second-line therapy after glucocorticoids includes immunosuppressant agents. Although the long-term outcome still remains unclear, there is increased interest in the relationships between IgG-RD and malignancies. In this review, the authors provide a detailed overview of the geoepidemiology, pathogenesis, diagnostic features, treatment, and prognosis of IgG4-RD.