Two thirds of the surface of our planet is covered by oceans, having an average depth of 3800 meters. An essential part of the marine biosphere is thus subjected to a major physical parameter: hydrostatic pressure. The aim of this comparative and functional genomic study is to characterize some of the mechanisms involved in the adaption to high hydrostatic pressure (HHP) of a hyperthermophilic piezophilic archaeon Thermococcus barophilus, isolated from a deep-sea hydrothermal vent. The genome of T. barophilus is composed of a 2 010 078 bp chromosome and of a 54,159 bp plasmid. This strain possesses one copy of 16S rRNA, one copy of 23S rRNA, two copies of 5S rRNA, but does not have 7S rRNA. Out of the 2315 hypothetical genes, 2265 encode proteins and 1184 have predicted functions. T. barophilus has 1124, 1165, 1436, 1283, 1307, 1209, 1149 and 1401 common genes (>60% d’identity) with T. gammatolerans, T. kodakaraensis, T. litoralis, T. onnurineus, T. sibiricus, T. sp 4557, T. sp. AM4 and T. sp. PK, respectively. 256 genes are unique to T. barophilus and do not have homologues in Thermococcales. Proteomic and transcriptomic analysis of T. barophilus, the sub- supraoptimal hydrostatic pressures : 0,1 and 70 MPa respectively modulate mainly the expression of proteins involved in certain metabolic pathways (transport and assimilation of certain amino acids and sugars) and unknown protein functions. This study has shown that the piezophilic archeon T. barophilus principally modulates the expression of genes involved in the assimilation of amino acids, sugars and energy production.