The Nam Ou Basin Profile is a collective effort among various stakeholders at the central, provincial, district, and village levels. The main objective of the Nam Ou River Basin Profile is to compile and present available background information on the Nam Ou Basin, one of the most important river systems in Lao PDR. It aims to provide baseline data for monitoring changes and comparing past and future trends for the planning and management of: (i) water resources allocation, (ii) hydropower development, (iii) community livelihoods, and (iv) emergency responses. The Profile was developed in collaboration with Government of Lao PDR water resource managers at the national, provincial and district levels. This compilation of data and information will further our understanding of the Nam Ou in relation to the Mekong River and the knowledge gained may be applied to other river basins and sectors in Lao PDR. Water basin managers around the country can use this Profile as a tool for developing a management plan for the Nam Ou Basin in the future. In addition to providing a comprehensive Profile of the Nam Ou River Basin, this document also includes conclusions and recommendations for further action.