This article presents an ecosystem perspective of riparian zones, emphasizing their role as interfaces between terrestrial and aquatic ecosystems. Riparian zones are ecotones with sharp environmental gradients and complex ecological processes. They are not easily defined but consist of mosaics of landforms, communities, and environments within the larger landscape. The authors propose a conceptual model integrating physical processes shaping valley-floor landscapes, terrestrial plant succession, habitat formation, and the production of nutrients for aquatic ecosystems. Riparian zones have been studied from various perspectives, leading to diverse and often confusing definitions based on hydrologic, topographic, edaphic, and vegetative criteria. These perspectives are ecologically incomplete and encourage rigid delineation of riparian boundaries. The importance of landscape perspectives for understanding stream ecosystems is highlighted, with recent concepts emphasizing the land-water interface as a source of organic and inorganic material for aquatic ecosystems. The authors define riparian zones functionally as three-dimensional zones of interaction between terrestrial and aquatic ecosystems. Boundaries extend outward to the limits of flooding and upward into the canopy of streamside vegetation. The dimensions of the zone of influence for a specific ecological process are determined by its unique spatial patterns and temporal dynamics. The article discusses the hierarchical structure of valley floor landforms, including active channels, floodplains, terraces, and alluvial fans. Geomorphic processes create a mosaic of stream channels and floodplains within the valley floor. These processes, along with disturbances from upland and fluvial origins, affect riparian zones, determining the spatial pattern and successional development of riparian vegetation. Riparian vegetation is dynamic and reflects histories of fluvial disturbance and non-fluvial disturbance regimes. The diversity of riparian plant communities is influenced by soil properties, topography, and disturbance regimes. Riparian zones support a high degree of structural and compositional diversity in plant communities. The article also discusses the role of riparian zones in nutrient cycling, including dissolved nutrient inputs, particulate terrestrial inputs, and retention of organic matter. Riparian vegetation influences the production of aquatic primary producers, the processing of organic matter, and the structure of aquatic invertebrate and vertebrate communities. Riparian zones are critical for the productivity of aquatic biota, providing food resources and habitats for fish and other aquatic organisms. The structure and composition of riparian zones influence the distribution and abundance of aquatic species, as well as the overall productivity of riverine ecosystems. The authors conclude that an ecosystem perspective of riparian zones is essential for understanding their role in landscape ecology and for managing riparian resources effectively. This perspective integrates physical processes, plant succession, and the structure and function of stream ecosystems to provide a rigorous ecological basis for riparian management.This article presents an ecosystem perspective of riparian zones, emphasizing their role as interfaces between terrestrial and aquatic ecosystems. Riparian zones are ecotones with sharp environmental gradients and complex ecological processes. They are not easily defined but consist of mosaics of landforms, communities, and environments within the larger landscape. The authors propose a conceptual model integrating physical processes shaping valley-floor landscapes, terrestrial plant succession, habitat formation, and the production of nutrients for aquatic ecosystems. Riparian zones have been studied from various perspectives, leading to diverse and often confusing definitions based on hydrologic, topographic, edaphic, and vegetative criteria. These perspectives are ecologically incomplete and encourage rigid delineation of riparian boundaries. The importance of landscape perspectives for understanding stream ecosystems is highlighted, with recent concepts emphasizing the land-water interface as a source of organic and inorganic material for aquatic ecosystems. The authors define riparian zones functionally as three-dimensional zones of interaction between terrestrial and aquatic ecosystems. Boundaries extend outward to the limits of flooding and upward into the canopy of streamside vegetation. The dimensions of the zone of influence for a specific ecological process are determined by its unique spatial patterns and temporal dynamics. The article discusses the hierarchical structure of valley floor landforms, including active channels, floodplains, terraces, and alluvial fans. Geomorphic processes create a mosaic of stream channels and floodplains within the valley floor. These processes, along with disturbances from upland and fluvial origins, affect riparian zones, determining the spatial pattern and successional development of riparian vegetation. Riparian vegetation is dynamic and reflects histories of fluvial disturbance and non-fluvial disturbance regimes. The diversity of riparian plant communities is influenced by soil properties, topography, and disturbance regimes. Riparian zones support a high degree of structural and compositional diversity in plant communities. The article also discusses the role of riparian zones in nutrient cycling, including dissolved nutrient inputs, particulate terrestrial inputs, and retention of organic matter. Riparian vegetation influences the production of aquatic primary producers, the processing of organic matter, and the structure of aquatic invertebrate and vertebrate communities. Riparian zones are critical for the productivity of aquatic biota, providing food resources and habitats for fish and other aquatic organisms. The structure and composition of riparian zones influence the distribution and abundance of aquatic species, as well as the overall productivity of riverine ecosystems. The authors conclude that an ecosystem perspective of riparian zones is essential for understanding their role in landscape ecology and for managing riparian resources effectively. This perspective integrates physical processes, plant succession, and the structure and function of stream ecosystems to provide a rigorous ecological basis for riparian management.