Swiftly moving sand or silt-laden water currents sometimes abrade grooves, elongated in the direction of flow, in stream boulders and in the bedrock of the stream channel. Discontinuous grooves of irregular pattern result from turbulence of the water flow. In this article the grooves are termed "flutes," and the process of their formation is called "stream fluting." The importance of stream fluting in fluvial erosion is discussed. The process is analyzed on the basis of excellent examples observed in the inner gorge of the Grand Canyon of the Colorado River.