The Danube River Basin is shared by 19 countries and there is no river basin in the world shared by so many nations. Covering an area of about 800,000 km², it is Europe's second largest river basin and home to 83 million people of different cultures, languages and historical backgrounds.Management of common water sources and overcoming difficulties caused by droughts and floods requires co-operation between these countries. In the past twenty years political turbulence has caused an increase in the number of countries included, making co-operation difficult at times. Nevertheless several projects were launched and a number of reports were produced. In 2008, at the 22nd Working Meeting of the Regional Hydrological Co-operation of the Danube Countries in the framework of IHP/UNESCO at the XXIVth Conference of the Danubian Countries, it was decided that these reports would be summarised in one special publication. It was also agreed to include additional reports serving the common interest.This publication therefore brings together the reports and papers related to regional co-operation. It is the result of a major collaboration and examines a broad range of topics. These include hydrological forecasting and hydro-meteorological extremes, global climate change and hydrological processes, water management, and developments in hydrology. The book includes the efforts of many hydrologists and technical staff from different Universities and Agencies from all countries of the Danube River Basin.