Shellfish can be a vector for human pathogens. Despite regulation based on enteric bacteria, shellfish are still implicated in viral outbreaks. Oysters are the most common shellfish associated with outbreaks, and noroviruses, which cause acute gastroenteritis, are the most frequently identified pathogen in these outbreaks. Analysis of shellfish-related outbreak data worldwide shows an unexpected high proportion of NoV GI strains. Recent studies performed in vitro, in vivo and in the environment indicate that oysters are not just a passive filter, but can selectively accumulate norovirus strains based on virus carbohydrate ligands shared with humans. These observations may help explain the GI/GII bias observed in shellfish-related outbreaks compared to other outbreaks