Soil erosion by water is a natural phenomenon that occurs on upland areas when soil is detached from a surface by impacting raindrops or by flowing water that exerts shear forces. This chapter will describe and discuss various soil erosion by water processes, particularly at agricultural field scale, and also elucidate current erosion process modeling technology and areas for future research. Multiple types of soil erosion by water can be described, usually with the dominant form changing as the scale of interest, including: 1.) Raindrop detachment, that includes splash erosion and rainfall-enhanced shallow flow transport, all of which are commonly called interrill erosion; 2.) Rill detachment, that can include headcut formation and advancement, excess flow shear erosion, sediment transport, sediment deposition in rill channels and/or divergent flow areas; 3.) Ephemeral gully erosion in concentrated flow channels, headcut formation and advancement, excess flow shear stress detachment, sediment transport, and sediment deposition.