Primary immunodeficiencies (PIDs) are a group of rare genetic diseases resulting in the impairment of one or more functions of the human immune system. Common variable immunodeficiency (CVID) is one of the most prevalent PIDs, yet despite extensive genetic analysis, most patients do not have a monogenetic diagnosis. This has led to the theory that CVID must be a polygenetic condition. An alternative theory to a monogenetic or polygenetic underlying cause of CVID is that it is epigenetic phenomena that are causal in the majority of CVID patients. I will briefly discuss epigenetic regulation in B-cell biology and development, current examples of epigenetic diseases causing CVID-like primary antibody deficiencies, and how these observations may guide future investigation into the role of epigenetics in CVID.