Phytobase is a relational database management system devoted to the management of vegetation survey data, following the concepts of the integrated synusial phytosociology. This 4D application has been developed from the 1990s and applied to various ecosystems (wood-pastures, forests, floodplains, wetlands and grasslands) in various regions, mostly in Switzerland and in France. Integrated synusial phytosociology considers that vegetation is organized in nested hierarchical levels, each of them being potentially described in a typological and classification system. The first, finest, level is the synusia, a concrete plant community composed of plant species co-occurring in a local similar environment, with comparable size and habitat use. Phytobase distinguishes three categories of synusiae, i.e. tree, shrub, herb and moss synusiae, classified into elementary syntaxa. They are eventually integrated into phytocoenoses, the second level of vegetation description, based on a list of synusial syntaxa co-occurring in a given phytocoenosis, such as a forest stand with its different layers, sylvogenetic phases and dependent (e.g. epiphytic) communities. Phytocoenoses are classified into elementary coenotaxa according to their synusial composition. Higher organization levels (tesela/sigmataxa and catena/geosigmataxa) are included in Phytobase as well, but only used so far for floodplain vegetation. The classification of synusiae is based on Julve’s ‘baseveg’ system. An automatic diagnostic of plot records is implemented in Phytobase, including classification in Julve’s system, assignment to an elementary syntaxon, ecological indicator values (Landolt, Ellenberg, Julve), life forms, Grime’s CSR strategies, functional traits, taxonomic diversity indices, pastoral value, etc. Each elementary syntaxon or coenotaxon is described by the centroid of all plot records that were assigned to it, and Phytobase includes various diagnostics for species (or elementary syntaxon) fidelity (IndVal, Phi, etc.), compositional homogeneity and ecology. Phytobase is freely available from the Tela-botanica website (http://www.tela-botanica.org/page:liste_projets?id_projet=18&act=documents&id_repertoire=16428), including a sample of relevés. It is used by more than two hundred registered users in Europe. The current version 8.3 has a user interface in French language but an English version is planned to allow a broader diffusion to the international community of vegetation scientists.