The universally conserved endoribonuclease P consists of one RNA subunit and, depending on its origin, a variable number of protein subunits. RNase P is involved in the processing of a large variety of substrates in the cell, the preferred substrate being tRNA precursors. Cleavage activity does not require the presence of the protein subunit(s) in vitro. This is true for both prokaryotic and eukaryotic RNase P RNA suggesting that the RNA based catalytic activity has been preserved during evolution. Progress has been made in our understanding of the contribution of residues and chemical groups both in the substrate as well as in RNase P RNA to substrate binding and catalysis. Moreover, we have access to two crystal structures of bacterial RNase P RNA but we still lack the structure of RNase P RNA in complex with its substrate and/or the protein subunit. Nevertheless, these recent advancements put us in a new position to study the way and nature of interactions between in particular RNase P RNA and its substrate. In this review I will discuss various aspects of the RNA component of RNase P with an emphasis on our current understanding of the interaction between RNase P RNA and its substrate.