A public-public partnership (PUP) is a collaboration between two or more public authorities or organisations, based on solidarity, to improve the capacity and effectiveness of one partner in providing public water or sanitation services. This new paper by PSI, PSIRU and TNI provides an overview of the typical objectives of PUPs; the different forms of PUPs and partners involved; a series of case studies of actual PUPs; and an examination of the recent WOPs initiative. It then offers recommendations for future development of PUPs. The paper includes an overview of over 130 PUPs in around 70 countries. This means that far more countries have hosted PUPs than host PPPs in water – according to a report from PPIAF in December 2008, there are only 44 countries with private participation in water.