The term RNA editing describes a diverse set of biochemical processes whereby genetic information is modulated on a post-transcriptional level i.e. on the level of ribonucleic acids (RNA). RNA editing has been demonstrated in viruses, protozoan organisms, in plants and in mammals and in many cases it has been identified as a key step in the regulation of gene expression. This book dedicates a chapter to each of the main types of RNA editing. All sections are written by experts in the various research areas and a specific focus is put on the correlation between RNA structure and function, as well as on the complex cellular machineries that catalyze the different editing reactions. This leads to a state of the art compendium of our current knowledge on RNA editing.