Water is essential for human survival and progress. In the Pacific, countries face a range of unique challenges resulting from the islands' size, topography, geology, location, and climate. The impact of these factors varies across and within countries, making generalizations difficult, although they result in similar resource concerns: water shortages, water and land use issues, and constraints on financial and human resources. To address some of these issues, the Asian Development Bank (ADB) assisted a number of its Pacific developing member countries in the area of water supply and sanitation. This special evaluation study reviews ADB's experience in four countries”Fiji Islands, Kiribati, Papua New Guinea (PNG), and the Republic of the Marshall Islands (RMI)”to assess how ADB support affected institutional performance and to draw lessons for ongoing and future assistance.