The Water Global Practice, under the WSSGSG Utility Turnaround thematic area, has implemented theGlobal Study on WSS Utility Aggregation to provideevidence-based guidance to policy makers and practitionersregarding when, why, and how water and sanitation utilitiescan work together ("aggregate") to successfullydeliver specific policy outcomes, such as better services orlower costs. This work builds on a review of existingliterature and an analysis of both qualitative andquantitative evidence, a global data set of internationaltrends, a utility performance database, and a series of casestudies. The deep-dive of 14 case studies of aggregationprocesses in seven countries (Brazil, Colombia, Hungary,Indonesia, Portugal, Mozambique, Romania) allowed conductinga qualitative analysis, by centering on the stakeholdersinvolved, the decisions made, the roles of sector actors andtheir incentives, and the perceived outcomes with a view tobringing forward the essence of each case experience. Theselection of the countries and specific providers was donein a manner to ensure a diversity of geography, developmentlevel, size, and aggregation design.