Malignant neoplasms or cancers of the B lymphocyte lineage are commonly called leukemias and lymphomas. B cell cancers primarily involve blood, lymphatic tissues, or bone marrow and arise due to acquired driver mutations at distinct stages of development and differentiation, followed by a clonal evolution process involving acquisition of additional driver mutations. Recent advances suggest that B cell development may be an intrinsically dangerous process due to the large number of cell divisions that occur during ontogeny, in addition to off-target mutations induced by expression of the mutagenic enzymes activation-induced cytidine deaminase and recombination-activating gene (RAG)-1/RAG-2. B cell cancers that will be considered in detail in this article include acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia, Hodgkin lymphoma, non-Hodgkin lymphomas, Waldenström's macroglobulinemia, and multiple myeloma. For each B cell neoplasm considered in this article, characteristics described will include incidence, classification schemes, mechanisms of transformation, cell of origin, and current treatments. Mechanisms of neoplastic transformation are discussed in detail for the example of precursor B-ALL.