<jats:p>Six obligately anaerobic bacterial isolates (195<jats:sup>T</jats:sup>, CBDB1, BAV1, VS, FL2 and GT) with strictly organohalide-respiring metabolisms were obtained from chlorinated solvent-contaminated aquifers, contaminated and uncontaminated river sediments or anoxic digester sludge. Cells were non-motile with a disc-shaped morphology, 0.3–1 µm in diameter and 0.1–0.2 µm thick, and characteristic indentations on opposite flat sides of the cell. Growth occurred in completely synthetic, reduced medium amended with a haloorganic electron acceptor (mostly chlorinated but also some brominated compounds), hydrogen as electron donor, acetate as carbon source, and vitamins. No other growth-supporting redox couples were identified. Aqueous hydrogen consumption threshold concentrations were <1 nM. Growth ceased when vitamin B<jats:sub>12</jats:sub>was omitted from the medium. Addition of sterile cell-free supernatant of<jats:italic>Dehalococcoides</jats:italic>-containing enrichment cultures enhanced dechlorination and growth of strains 195 and FL2, suggesting the existence of so-far unidentified stimulants. Dechlorination occurred between pH 6.5 and 8.0 and over a temperature range of 15–35 °C, with an optimum growth temperature between 25 and 30 °C. The major phospholipid fatty acids were 14 : 0 (15.7 mol%), br15 : 0 (6.2 mol%), 16 : 0 (22.7 mol%), 10-methyl 16 : 0 (25.8 mol%) and 18 : 0 (16.6 mol%). Unusual furan fatty acids including 9-(5-pentyl-2-furyl)-nonanoate and 8-(5-hexyl-2-furyl)-octanoate were detected in strains FL2, BAV1 and GT, but not in strains 195<jats:sup>T</jats:sup>and CBDB1. The 16S rRNA gene sequences of the six isolates shared more than 98 % identity, and phylogenetic analysis revealed an affiliation with the phylum<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="class" xlink:type="simple"><jats:ext-link ext-link-type="uri" xlink:href="http://dx.doi.org/10.1601/nm.550" xlink:type="simple"><jats:italic>Chloroflexi</jats:italic></jats:ext-link></jats:named-content>and more than 10 % sequence divergence from other described isolates. The genome sizes and G+C contents ranged from 1.34 to 1.47 Mbp and 47 to 48.9 mol% G+C, respectively. Based on 16S rRNA gene sequence comparisons, genome-wide average nucleotide identity and phenotypic characteristics, the organohalide-respiring isolates represent a new genus and species, for which the name<jats:italic>Dehalococcoides mccartyi</jats:italic>gen. nov., sp. nov. is proposed. Isolates BAV1 ( = ATCC BAA-2100  = JCM 16839  = KCTC 5957), FL2 ( = ATCC BAA-2098  = DSM 23585  = JCM 16840  = KCTC 5959), GT ( = ATCC BAA-2099  = JCM 16841  = KCTC 5958), CBDB1, 195<jats:sup>T</jats:sup>( = ATCC BAA-2266<jats:sup>T</jats:sup> = KCTC 15142<jats:sup>T</jats:sup>) and VS are considered strains of<jats:italic>Dehalococcoides mccartyi</jats:italic>, with strain 195<jats:sup>T</jats:sup>as the type strain. The new class<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="class" xlink:type="simple"><jats:ext-link ext-link-type="uri" xlink:href="http://dx.doi.org/10.1601/nm.21205" xlink:type="simple"><jats:italic>Dehalococcoidia</jats:italic></jats:ext-link></jats:named-content>classis nov., order<jats:italic>Dehalococcoidales</jats:italic>ord. nov. and family<jats:italic>Dehalococcoidaceae</jats:italic>fam. nov. are described to accommodate the new taxon.</jats:p>