The diversity of mucin-degrading bacteria in the human intestine was investigated by combining culture and 16S rRNA-dependent approaches. A dominant bacterium, strain Muc^T, was isolated by dilution to extinction of faeces in anaerobic medium containing gastric mucin as the sole carbon and nitrogen source. A pure culture was obtained using the anaerobic soft agar technique. Strain Muc^T was a Gram-negative, strictly anaerobic, non-motile, non-spore-forming, oval-shaped bacterium that could grow singly and in pairs. When grown on mucin medium, cells produced a capsule and were found to aggregate. Strain Muc^T could grow on a limited number of sugars, including N-acetylglucosamine, N-acetylgalactosamine and glucose, but only when a protein source was provided and with a lower growth rate and final density than on mucin. The G+C content of DNA from strain Muc^T was 47·6 mol%. 16S rRNA gene sequence analysis revealed that the isolate was part of the division Verrucomicrobia. The closest described relative of strain Muc^T was Verrucomicrobium spinosum (92 % sequence similarity). Remarkably, the 16S rRNA gene sequence of strain Muc^T showed 99 % similarity to three uncultured colonic bacteria. According to the data obtained in this work, strain Muc^T represents a novel bacterium belonging to a new genus in subdivision 1 of the Verrucomicrobia; the name Akkermansia muciniphila gen. nov., sp. nov. is proposed; the type strain is Muc^T (=ATCC BAA-835^T=CIP 107961^T).