The development of agents capable of cleaving RNA and DNA has attracted considerable attention of researchers in the last few years, because of their application in biotechnology and pharmacology. Artificial nucleases are rationally designed to imitate the active centers of natural enzymes by simple structures possessing minimal sets of the most important characteristics that are essential for catalysis. Being less efficient and specific than natural enzymes, the primitive mimics are smaller, more robust and able to function in a broad range of conditions. The authors of the present volume summarize the state of the art in the rapidly developing field of artificial nucleases. The chapters deal with mechanisms of RNA and DNA cleavage by chemical agents and natural enzymes, development of new nucleic acid-cleaving agents, applications of artificial nucleases, and design of oligonucleotide conjugates with RNA- and DNA-cleaving agents.