We present the first public release of PhEVER, a unique database of homologous gene families containing sequences (i) of all completely sequenced viruses and (ii) from fully sequenced cellular organisms. The protein sequences are clustered-without a priori and according to similarity criteria-into families containing either only viral sequences or both viral and cellular sequences. PhEVER integrates extensive data from up-to-date completely sequenced genomes spanning a wide taxonomic range (2426 non-redundant viral genomes, 1007 non-redundant prokaryotic genomes, 43 eukaryotic genomes ranging from plants to vertebrates). To our knowledge, this is the most complete database of families of homologous viral sequences. Indeed, it not only spans all known viral groups but it also has the unique feature of presenting homologies with eukaryotic and prokaryotic sequences. The database offers a clustering of proteins into homologous families containing at least one viral sequence, as well as pre-computed alignments and phylogenies for each of these families. Alignments and phylogenies are built according to state-of-the-art phylogeny procedures and we provide tools to edit them and recompute them on the fly (14) . We also provide the possibility for users to assign their sequence of interest to a family and to re-build the phylogeny accordingly through the HoSeqI tool (15) . PhEVER thus constitutes a comprehensive working tool to detect sequence homologies and possible gene transfer events. Public access and documentation is available through the database webpage and through all dedicated ACNUC retrieval systems (16) .