Using whole exome sequencing to examine the genetic causes of immune deficiency in 235 CVID patients seen in New York, 128 patients from Sweden, and 208 from Iran, revealed 73 known disease-causing genes associated with this heterogeneous immune defect. The patients at the time of study ranged from age 4 to age 90. Overall, for 31%, 36% and 54% of the patients in United States, Swedish or Iranian cohorts, mutations were identified. The multiplicity of genes identified reflects the complex requirements of B cell antigen signaling, activation, survival, migration, maturation and maintenance of antibody-secreting memory B cell populations to the plasma cell stage. For the United States and Swedish cohorts, CVID subjects with non-infectious complications, lymphoid infiltrations, inflammatory, or autoimmunity, were more likely to have an identifiable gene, but in both cohorts, numerous subjects with these medical conditions had no potential gene that could be assigned. Specific clinical patterns of illnesses were also not linked to any given gene defect as there was considerable overlap in clinical presentations. These observations provide a broad perspective on the complexity of the genetic and immunologic phenotypes found in 571 CVID subjects of different ages and backgrounds.