Prolyl endopeptidases, or post-proline-cleaving enzymes, are the specific endopeptidases that hydrolyze peptide substrates at the carbonyl of the internal Pro residue. All the currently known prolyl endopeptidases from animals, microorganisms, fungi, and plants as well as the post-proline-cleaving enzymes that do not exhibit the strict specificity to Pro are reviewed. The data on their physicochemical and catalytic properties, substrate specificity, inhibitors, sequences, and three-dimensional structures are discussed.