B lymphopoiesis is a differentiation process in which hematopoietic stem cells are converted into antibody-producing plasma cells. B cell differentiation involves multiple steps, including cell specification, commitment to the B cell lineage, immunoglobulin rearrangements, maturation of B cells and terminal differentiation into plasma cells. Each of these steps is controlled by signaling pathways and transcription factors that act in synergy. feedback-loops or cross-antagonism to Generate complex regulatory networks that allow for plasticity and stability of B cell differentiation. (c) 2005 Elsevier Ltd. All rights reserved.