Headwater streams consist of ephemeral, intermittent, and permanent water courses that are at the interface of the aquatic-terrestrial continuum.  Despite their concealed nature, headwater streams and associated catchments make up the bulk of watersheds by area, and they make up the bulk of riverine habitats by length.  Consequently, the ecological integrity of headwater systems may have important influences on the ecological integrity of the entire downstream riverine continuum.  Headwaters differ widely in their physical, chemical, and biotic attributes, and provide habitats for a range of unique species, thereby contributing to the overall biodiversity of a river system. Headwater species include permanent residents as well as migrants that travel to headwaters at particular seasons or life stages. Additionally, retention and export of materials in headwater streams (emergent and drifting insects, detritus, sediment, nutrients) play key roles in structuring downstream river ecology and adjacent terrestrial ecosystems.  Degradation and loss of headwaters and their connectivity to ecosystems downstream threaten the biological diversity of entire river networks.  In this symposium, we will explore the diversity in headwater systems across North America and how these unique systems interact with downstream rivers and their terrestrial ecosystem at a watershed scale. To assist us we have gathered speakers across a wide range of geographies (Great Plains, Atlantic, Pacific and Gulf Coasts, Appalachians, and Rocky Mountains) and systems (Deserts, Forests, Grasslands, Urban, and Coastal Plains).