This article presents an historical perspective of the controversy concerning the hydrological impact of forests, and shows how a mostly romantic and emotional confrontation finally evolved into a scientific debate. We first analyze the historical evolution of ideas, starting with the views of Pliny the Elder in the first century A.D. and ending with the debate on the "Eaux et Forêts" in France in the 19th century. Then, we give an up-to-date overview of the paired-watershed experiments conducted throughout 20th century, and identify some research issues that should help forest hydrology science to move forward in the 21st century.