Expression of activation-induced cytidine deaminase (AID) by germinal center (GC) B cells drives the processes of immunoglobulin (Ig) somatic hypermutation (SHM) and class switch recombination (CSR) necessary for the generation of high affinity IgG serum antibody and the memory B-cell compartment. Increasing evidence indicates that AID is also expressed at low levels in developing B cells but to date, this early, developmentally regulated AID expression has no known function. Does the timing and extent of AID expression in developmentally immature, non-GC B cells provide clues to reveal its physiologic role?