A literature review is presented for erosion of surfaces by water-drop impact. The types of experimental apparatus employed are discussed and include the vibratory method, and the wheel-and-jet, rotating-arm, interrupted-jet, and shock-wave apparatus. Factors discussed which determine the extent of erosion are temperature, time, drop velocity and shape, specimen velocity and shape, drop size and material, specimen size and material, blemishes, and protective finishes and coatings. The results of microscopic and x-ray studies are discussed. Liquid-solid-impact discussions include the steps in drop collapse, pressure under an impacting water drop, and the results of shock-wave studies. A review of the erosion process includes studies of fatigue ranges, the chemical and mechanical nature of erosion, initiation centers, and erosion mechanisms.