AbstractMetal(II)‐induced hydrolysis of RNA produce products with 5′‐hydroxyls and 2′;3′‐cyclic phosphates at the ends. Ribozymes are RNA molecules that act as catalysts. Some ribozymes that cleave RNA also generate 5′‐hydroxyls and 2′;3′‐cyclic phosphates whereas others produces 5′‐phosphates and 3′‐hydroxyls at the ends of the cleavage products. RNase P is an essential endoribonuclease involved in RNA processing. The catalytic RNA subunit of RNase P is a trans‐acting ribozyme that cleaves various RNA substrates in vitro generating 5′‐phosphates and 3′‐hydroxyls as cleavage products. The activity depends on the presence of metal(II) ions such as Mg2+. RNase P RNA has therefore to facilitate a nucleophilic attack that generates the correct product ends and prevent metal(II)‐induced hydrolysis of the RNA substrate. In this review, we will discuss our current understanding of the interactions between RNase P RNA and its substrate, role of specific residues with respect to catalysis and positioning of functionally important Mg2+ at and in the vicinity of the cleavage site that ensures that products with correct ends are generated. Moreover, we will discuss the composition of RNase P and its RNA subunit in an evolutionary perspective. © 2009 IUBMB IUBMB Life, 61(3):189–200, 2009