B-cell development is characterized by antigen-independent phases in fetal hematopoietic organs and adult bone marrow, which lead to naive recirculating B cells in the periphery. The diversity of the naive (primary) B-cell repertoire resides in somatic events where minigenes from a large available repertoire are imprecisely rearranged and encode antigen-binding sites of antibodies. Naive B cells expand upon antigenic stimulation, acquire somatic mutations leading to high-affinity antibodies, and switch immunoglobulin (Ig) isotype in peripheral lymphoid organs. This immune reaction leads to the generation of memory B cells, which are long-lived and capable of rapid generation of specific high-affinity antibodies upon recall antigenic stimulation, as well as plasma cells, which constitutively secrete a large amount of antibodies.