Corridor was once used primarily to describe an architectural feature, a passageway connecting two separate buildings, but recently it has taken on a broader, conceptual meaning as an area that distinguishes itself from its surroundings by either the access or passage it provides. We now speak of air, recreational, transportation, environmental, high-tech, economic, migratory, retail, stream, and heritage corridors. Greenway corridors made up of streams, ﬂoodplains, open space, and woods in cities and suburbs are essential for the survival of native animal and plant species, the maintenance of ecosystems, and the preservation of geological formations. Organizations such as the Lackawanna River Corridor Association in northeast Pennsylvania and the Mississippi Corridor Neighborhood Coalition in Minneapolis have formed to protect and advocate for degraded and endangered rivers that pass through their communities. The Springwater Corridor in Portland, Oregon, is a railto-trails project that has created 170 miles of recreational pathway for hikers, joggers, and bicyclists.