Common variable immune deficiency (CVID) is a clinically and immunologically heterogenous primary immune deficiency first described more than 50 years ago. The main features are hypogammaglobulinemia, recurrent infections, and other complications. While CVID is considered as a genetic immune defect, and several genes have been reported as leading to the CVID phenotype, one of the most puzzling features of CVID is the sporadic inheritance pattern and the relatively late onset. In most cases, no other family members have any immune defect. The mean age at diagnosis is between 25 and 45 years of age. These features suggest the interplay between either several or numerous genes with or without potential environmental factors.