Twelve mitochondrial mRNAs are edited in Trypanosoma brucei, nine extensively, by addition and removal of uridines. The accumulation of the edited RNAs is regulated during the life cycle. Hundreds of different gRNAs, encoded three or four per minicircle, specify the editing and minicircle content accounts for variation in editing among species and in mutants. The current understanding of the process of gRNA utilization, the editing mechanism and the editing machinery is discussed.