This report considers the ways and means of optimising relations between levels of government (supranational, national and subnational) in terms of the quality of regulation. It draws on many OECD studies, though the information they contain has to date been only rarely treated from the standpoint of multilevel governance. Today, however, the growing role of supra- and subnational levels presents governments with new challenges, to which a suitable regulatory framework could help to provide answers. This report is exceptionally provided in both English and French. The French version "La gouvernance réglementaire multi-niveaux" follows immediately behind the English version of the report.