Résumé : The main purpose of this chapter is to argue that the optimal design of regulation of water and sanitation monopolies should be the outcome of a detailed diagnostic of the institutional constraints impacting the ability of the operator - whether public or private - to deliver the services.Tailoring the regulatory processes and instruments to account for institutional and informational weaknesses stands a better chance of improving the performance of the sector than the adoption of imported standardized or pre-packaged regulatory tools.