The expedition to explore the sources of the main rivers of European Russia was conducted under the guidance of A.A. Tillo in 1894-1902. Its main task was to gather information about the sources and conditions of feed of the upper fl ow of the largest rivers of this territory – Oka, Volga, Western Dvina, Dnieper, Don and their tributaries. The purpose of the expedition was to develop practical measures to improve the regulation of water content of rivers. The main result of the research was the draft water law, which was enacted in 1900-ies. The extensive materials published in the form of reports and monographs under the heading of the Expedition were collected during the fi eld survey. Many of these works became fundamental to the development of geography and especially hydrology in Russia and in demand to date.