Common variable immunodeficiency (CVID) is one of the most common primary immunodeficiency (PID) that is categorized into primary antibody deficiency. Diagnosis is made by excluding all the other conditions and PID that lead to hypo-gamma-globulinemia. About 30-50% of the CVID patients show autoimmunity as well as malignancy in their course. Responsible genes identified so far include ICOS, TACI, CD19, CD20, CD21, CD81, BAFF-R, MSH5, PLCD2, and LRBA; and most of the CVID-causing genes are yet to be identified. It is of importance to develop appropriate diagnostic measure, establish CVID classification that would predict clinical outcome, identify the disease causing genes, and eventually to develop the optimal therapy.