Robert Elmer Horton (May 18, 1875 - April 22, 1945) was an American ecologist and soil scientist, considered by many to be the father of modern hydrology.

Born in Parma, Michigan, he earned his B.S. from Albion College in 1897. After his graduation, he went to work for his uncle, George Rafter, a prominent civil engineer. Rafter had commissioned a weir study, the results of which Horton analyzed and summarized. In 1900, he was appointed New York District Engineer of the United States Geological Survey.

During his studies of New York streams, Horton determined that the degree to which rainfall could reach the aquifer depended on a certain property of the soil, which he called infiltration capacity. He analyzed and separated the water cycle into the processes of infiltration, evaporation, interception, transpiration, overland flow, etc. Horton was the first to demarcate and label these now-familiar stages of the cycle.

Horton is well known for his study of maximum runoff and flood generation. His concept of maximum possible rainfall, limiting the effect of rainfall in specific regions, has had a major effect on meteorology. His studies of overland flow aided in the understanding of soil erosion and provided a scientific basis for soil conservation efforts.