Common variable immunodeficiency (CVID) is a rare immune deficiency characterized by low levels of serum IgG, IgA, and/or IgM, with a loss of Ab production. The diagnosis is most commonly made in adults between the ages of 20 and 40 years, but both children and much older adults can be found to have this immune defect. The range of clinical manifestations is broad, including acute and chronic infections, inflammatory and autoimmune diseases, and an increased incidence of cancer and lymphoma. For all of these reasons, the disease phenotype is both heterogeneous and complex. In the past few years, data from large patient registries have revealed that both selected laboratory markers and clinical phenotyping may aid in separating groups of subjects into biologically relevant categories. CVID consists of 2 phenotypes, 1 in which infections are the characteristic and another in which impressive inflammatory and/or hematologic complications also develop, including lymphadenopathy, splenomegaly, autoimmune cytopenias, enteropathy, and/or and granulomatous disease. These phenotypes appear to be stable, are related to immunologic and inflammatory markers, and are predictive of outcomes. This review outlines current understanding about this syndrome based on studies of large cohorts, highlighting the evaluation and treatment of complications and, in particular, the autoimmune and inflammatory conditions that affect these patients.