With a population of probably less than 50 individuals, the Slender-billed Curlew is one of the most seriously endangered species in Europe. The scarcity of information on its biology and the fact that its breeding grounds are still unknown are major constraints on its conservation. This paper presents the activities of the Working Group established under the Bonn Convention. Recent intensive efforts to locate breeding areas are described. All records are kept in a specific BirdLife International database. Although hunting is considered to have been the major reason for the species' dramatic decline and is still an important threat, overgrazing of steppes and drainage of wetlands in northern Kazakhstan and south-western Siberia have caused the loss of a number of possible breeding sites recently identified.