This review discusses progress made over the past 10+ years in elucidating the properties, regulation, and function of protein tyrosine phosphatase alpha (PTPα). It is apparent from studies in knockout mice and diverse cell lines that the major action of PTPα is as a positive regulator of src and src family kinases. PTPα dephosphorylates and activates src. In this manner it affects transformation and tumourigenesis, inhibition of proliferation and cell cycle arrest, mitotic activation of src, integrin signaling, neuronal differentiation and outgrowth, and ion channel activity. PTPα may well modulate additional processes, including insulin signaling, and have other targets besides src family kinases. As an important modulator of several specific cell signaling pathways, PTPα has promise as a target for drug discovery. Continued research on the physiological and pathological activities of PTPα is necessary to define the therapeutic potential of PTPα-directed pharmacologicals.