Riparian corridors are integrated ecological units characterized by a diversity of aquatic and terrestrial habitats sustained by fluvial dynamics. Intact riverine corridors provide critical habitat for diverse biotic communities, the species being arrayed along multidimensional environmental gradients. This paper reviews some aspects of biodiversity in this context. Specifically, we address four aspects deemed essential for understanding biodiversity patterns along and within riparian corridors: (1) linking terrestrial and aquatic biodiversity, (2) distinguishing the different components of biodiversity, with an emphasis on the value of beta diversity, (3) establishing a hierarchical framework for examining biodiversity, and (4) identifying the relative importance of regional and local processes in structuring diversity. In addition, we present a major research programme recently initiated to investigate biodiversity along the last morphologically intact riparian corridor in the Alps, the Fiume Tagliamento in NE Italy. Results from an analysis of structural diversity at different scales in the Tagliamento provide insight into the hierarchy of factors that may be responsible for the generation and maintenance of biodiversity.