Protein splicing is a post-translational autocatalytic excision of internal protein sequence (intein) with the subsequent ligation of the flanking polypeptides (exteins). This process doesn't require any cofactors or enzymes, which distinguish it from other variants of protein processing. Protein splicing is catalyzed by Hint-domain - internal intein's domain. In review the main molecular mechanisms of this process are described. Function of analogous Hint-domains of other proteins families (Hh-proteins, BIL-domains etc) are considered. The analysis of inteins characteristic to different branches of life illustrates the role of horizontal transfer in intein's distribution and evolution. A possible role of inteins in regulation of different cell processes is discussed.