Title: An Institutional Assessment of Irrigation Systems: A Case Study in the Lake Tana Basin, Ethiopia Surname, Name: Idil, Ires Abstract Following the Ethiopian Water Resources Management Policy (WRMP) issued in 1998, the government focused on decentralization and increasing the user community participation in the rural-centralized water resources planning, development and management. Under this strategy Water Users Associations (WUAs) are established to create a well-functioning decentralized, participatory system, as well as to be in charge of fee collection, operation and maintenance of the irrigation systems. Koga Irrigation System in the Lake Tana Basin is a pilot large scale project implemented under these aims. The significance of this project is underlined by government because the construction of several similar systems are dependent on it’s success, while the success of the project is dependent on the compliance of the farmers with the new established rules and participation in the WUAs. Different sets of rules affect the decisions and behaviors of users differently. One way to overcome CPR problems and achieve a robust and sustainable resource management is to attain the seven Design Principles (Ostrom 1990; Ostrom et. al. 1994; Ostrom and Benjamin 1993). These principles can be reflected by rules-in-use and the related seven clusters of variables in the action situation of Institutional Analysis and Development (IAD) Framework (Ostrom 1990; Ostrom et al. 1994; Ostrom and Polski 1999), where the interactions of different community attributes, rules-in-use, biophysical conditions and actors lead to different variables of outcomes, and therefore have different impacts on performance. The study compares the new sets of rules with the old ones and aims to find out the restrictions and limitations of the new rules, which do not comply with the resource characteristics and create obstacles in the resource management. The IAD Framework is methodologically used to bring the aspects together, evaluate the interactions and to anticipate the alternatives or combined institutions that would result with better outcomes. Keywords: Water Use Associations, rules, performance, compliance, irrigation systems