This document presents the framework for the implementation of the hydrological observing system of the Volta River Basin, called Volta-HYCOS. It was prepared on the basis of a draft document written in 2003 by the World Meteorological Organization (WMO), with the assistance of IRD (French Institute of Research and Development) under the new strategy adopted by the WMO to execute the West and Central Africa AOC) – HYCOS project in components corresponding to large river basins in the sub-region.