Vaccines and therapies to prevent and treat Norovirus infections are not available, despite the worldwide prevalence of Norovirus infections. Outbreaks of human gastroenteritis attributable to Norovirus commonly occur in group settings, such as hospitals, nursing homes, schools, dormitories, cruise ships and military barracks. This application claims isolated VHH monoclonal antibodies that specifically bind to a Norovirus polypeptide. Llama-derived single chain antibody fragments (also called VHH) are small, recombinant monoclonal antibodies of 15 kDa (“nanobodies”) with several advantages over conventional antibodies. The antibodies that were derived from llamas showed strong neutralizing activity against Norovirus in in vitro assays. These nanobodies may have application as immunoprophylaxis to protect individuals from infections or as a possible treatment for infected individuals, or can be used to develop a diagnostic for detection of norovirus infections, and may be potentially utilized in vaccine research.