This book provides the first and only comprehensive description and detailed summary of the genetics, structure, function, mechanisms of action, evolution and engineering of homing endonucleases and inteins. These two unique protein superfamilies, which are tied together through their frequent fusion and coevolution, have generated considerable excitement for their fundamental, structural, and functional properties, their evolution as parasitic elements, and their widespread applications as gene targeting agents and as instruments for the generation of modified proteins and novel protein combinations.