This volume details our current understanding of the architecture and signaling capabilities of the B cell antigen receptor (BCR) in health and disease. The first chapters review new insights into the assembly of BCR components and their organization on the cell surface. Subsequent contributions focus on the molecular interactions that connect the BCR with major intracellular signaling pathways such as Ca 2+ mobilization, membrane phospholipid metabolism, nuclear translocation of NF-kB or the activation of Bruton’s Tyrosine Kinase and MAP kinases. These elements orchestrate cytoplasmic and nuclear responses as well as cytoskeleton dynamics for antigen internalization. Furthermore, a key mechanism of how B cells remember their cognate antigen is discussed in detail. Altogether, the discoveries presented provide a better understanding of B cell biology and help to explain some B cell-mediated pathogenicities, like autoimmune phenomena or the formation of B cell tumors, whilealso paving the way for eventually combating these diseases.