Fifteen years after the launch of ERS-1 and TOPEX/POSEIDON, the European Space Agency, in collaboration with the French Space Agency, CNES, is organising an exceptional Symposium on "15 Years of Progress in Radar Altimetry", in Venice, from 13 to 18 March 2006. This unique event will create the opportunity to look back and analyse the progress made since the launch of ERS-1, characterise the difficulties, learn from the ones overcome and focus on the unresolved issues. This Symposium will host a very rich Hydrology session which will acknowledge the important progress recently made in radar altimetry retrieval algorithms. This permitted the reprocessing of data since the launch or ERS1 and offers to the non-specialist of radar altimetry a surface water level time series up to 15 years long, globally. Furthermore while large remote basins have very few, and often inaccurate or incomplete observations available to validate models, these times series are being used to better understand the strengths and weaknesses of hydraulic models, as well as the limitations of such data series. Requirements for the future altimetric missions, in particular the Water Elevation Recovery mission (WatER) proposed to ESA by an international team, are scheduled to be presented and discussed in a special session followed by a round table session.