Mammalian c-Abl belongs to an evolutionary conserved family of non-receptor tyrosine kinases. It is distributed both in the cytoplasm in association with F-actin, and in the nucleus where it binds chromatin. The normal function of c-Abl is poorly understood. Nevertheless, there has been rapid progress in the characterization of the structural features, signal transduction pathways, substrates and ligands involved in the action of c-Abl and Abl-derived oncogenes. These developments suggest that several mechanisms co-operate to allow regulation of normal cell growth by c-Abl and induction of leukemias by Bcr-abl.