No abstracts are to be cited without prior reference to the author.The EUNIS habitat classification has been developed on behalf of the European Environment Agency to facilitate description of marine and terrestrial European habitats through the use of criteria for habitat identification. It is a broadly-based hierarchical classification which provides an easily understood common language for habitats. It builds on earlier initiatives (CORINE and Palaearctic habitat classifications) and incorporates existing classifications used by European marine Conventions and the EU-funded BioMar project with cross-references to these and other systems. It is recognised that detailed biotopes from some marine regions are poorly represented and that EUNIS will need to be expanded to cover this wider geographic area. Most of the additions will probably be made at hierarchical level 5 (where the distinct BioMar and Mediterranean units are now held). Changes and additions to the classification will only be made following detailed consultation with experts. A key to the habitat units at each of the first three levels is incorporated and the classification is linked to a parameter-based database to describe specific habitats. The present draft of the EUNIS habitat classification was completed in November 1999 and is expected to remain stable for a time to allow validation and testing through field trials and descriptive parameters to be compiled.