The results of a study of Irish Lolio-Potentillion communities are presented in this paper. The syntaxonomical and synecological position of the following communities are described: 1. Basal community of Agrostis stolonifera-[Lolio-Potentillion anserinae] a) Lolium perenne-Juncus inflexus type b) Juncus articulatus-Galium palustre type 2. Nasturtio-Alopecuretum geniculati a) stellarietosum alsinis subass.nov. b) ranunculetosum scelerati subass.nov. 3. Triglochino-Agroslietum stoloniferae a) subassociation ranunculetosum repentis b) subassociation juncetosum gerardii c) subassociation inops 4. Agrostio-Trifolietum fragiferi a) subassociation inops b) subassociation festucetosum rubrae The relations of the communities to the two main environmental factors determining the internal differentiation within the Lolio-Potenlillion are discussed on the basis of ordination diagrams.