The naturally occurring dipeptide carnosine (β-alanyl-l-histidine) was discovered more than 100 years ago. Since then, many physiological functions have been ascribed to it but its biological role still remains enigmatic. Among its remarkable features, its potential to inhibit the growth of neoplastic cells has gained increasing attention during the last two decades, and new experimental data have opened a windows for a deeper understanding on the physiological mechanisms responsible for carnosine's antiproliferative potential in cancer cells. In this chapter we will discuss recent data on the antitumor activity of carnosine on the background of other investigations of its physiological role. The possible involvement of signal-transduction pathways and mechanisms of glycolytic control, the control of apoptosis and of cell-cycle regulation are discoursed, and finally, considerations with regard to a therapeutic use of carnosine are discussed.