Pancreatic ribonuclease, the focus of highly productive scientific research for more than half a century and the only enzyme to be the basis of four Nobel prizes, has recently undergone a resurgence in popularity for the recognition of an extended ribonuclease superfamily with functions ranging from tumor growth and inhibition to self-recognition and neurotoxicity. This volume highlights the functional diversity of ribonucleases and reveals the emerging research opportunities provided by these enzymes.