RNA editing is a process in which sequence information changes at the level of RNA after or during its transcription. It was first revealed by the posttranscriptional insertion and deletion of non-encoded uridines into the mitochondrial RNA of trypanosomes. RNA editing have been described in organisms from unicellular protozoa to man, and can affect the mRNAs, tRNAs, and rRNAs present in all cellular compartments. It involves several unrelated mechanisms as the insertion and deletion of nucleotides and the conversion of one base to another. This leads to changes in amino acids, creation of termination or initiation codons, new open reading frame and may also affect RNA maturation or splicing. Recent identifications of some enzymes, such as deaminases, and proteins implicated in RNA editing have provided a better understanding of its functional consequences in human physiology, the parasite cycle or viral replication.