CD37 belongs to the tetraspanin family of transmembrane proteins and a high level of expression is restricted largely to normal and as well as malignant B cells. Other immune cell populations such as T cells and monocytes, however, have been shown to express low levels of CD37. While the molecular mechanisms are still not fully resolved, research studies have shown that CD37 becomes tyrosine phosphorylated and facilitates association with intracellular signaling proteins that drive both survival and apoptosis in B cells. Due to its fairly restricted, high level of expression in normal and neoplastic B cells, CD37 has become an attractive immunotherapy target in the context of B cells malignancies.