This Catalogue includes the taxonomic units of the native and exotic taxa, both adventice and cultivated of the vascular flora of Sicily. Species and subspecies, as well as varieties and forms are taken into consideration, contrary to the actual tendency to include only the former. The main aim of the Catalogue is therefore to analyze the flora of the largest and significant island of the Mediterranean, and to give a tool for specialists of the field and an informative basis of the regional biodiversity in favour of preserving and promoting actions. Together with synonymic information on each single taxon, the Catalogue includes ecological and distributive references of the region. Nomemclatural novelties and the descriptions of new taxa are also included. Taxa referring to naturalized or cultivated native and exotic plants, which are widely sponta- neous, are numbered. Non numbered problematic taxa are also reported. Bibliography is given for each taxonomic unit. The Catalogue includes in total 176 families, 878 genera, and 3201 specific and infra-specific taxa (subspecies, varieties and forms) excluding doubtful and extinct ones as well as exotic cul- tivated.