Abstract: The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of specific ruthenium catalysts or pre-catalysts in hydrogenation processes for the reduction of ketones, aldehydes, esters or lactones into their corresponding alcohols or diols respectively. The preferred catalysts are ruthenium complexes comprising a ligand of the type (N—N) type and a ligand of the type (P—PO).