Small streams make up 70%-80% of the total channel length of river networks, and they strongly influence downstream portions these networks. The role small streams ? known as headstreams ? play in retaining or transmitting sediment and nutrients, providing habitat and refuge for diverse aquatic and riparian organisms, creating migration corridors, and governing connectivity at the watershed-scale is the subject of a review by Ellen Wohl of Colorado State University in the US. The article is published in a special issue on Headwater Regions in the journal Frontiers of Earth Science, which is jointly published by Higher Education Press in China and Springer.