B cells belong to a group of white blood cells known as lymphocytes, making them a vital part of the immune system. The human body makes millions of different types of B cells each day that circulate in the blood and lymphatic system performing the role of immune surveillance. They do not produce antibodies until they become fully activated. In this book, the authors present current research in the study of the molecular biology, developmental origin and impact on the immune system of B cells. Topics discussed include the role of B cells in intracellular bacterial pathogen infections; dynamic clustering of BCR-lipid rafts in antigen affinity discrimination by B cells; and B cells as a key player in the pathogenesis of multiple sclerosis.