A formalized and supervised phytosociological classification of Alnion glutinosae and Alnion incanae in the Czech Republic is presented. Three associations of Alnion glutinosae (Thelypterido palustris-Alnetum glutinosae, Carici elongatae-Alnetum glutinosae and Carici acutiformis-Alnetum glutinosae) and seven of Alnion incanae (Alnetum incanae, Stellario nemorum-Alnetum glutinosae, Pruno-Fraxinetum, Carici remotae-Fraxinetum, Piceo-Alnetum, Ficario-Ulmetum campestris and Fraxino pannonicae-Ulmetum) were distinguished by the Cocktail method using sociological species groups. Information about their syntaxonomy, species composition, ecology and distribution is presented. Ellenberg’s indicator values were used to show the main ecological gradients responsible for the variation in the vegetation of these communities. The most important factors affecting this variation were temperature (for Alnion incanae) and soil reaction, nutrient availability and moisture (for Alnion glutinosae).