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Noroviruses are now recognized as important causes of illness, and their incidence, impact, or both appear to have changed in recent years. This review focuses on studies that provide new knowledge needed to understand their transmission, pathogenesis, evolutionary changes and options for control.Noroviruses have become important causes of hospitalization for gastroenteritis in children worldwide, with prevalences and clinical impact in the same range as those observed for rotaviruses – contrary to earlier findings. The repertoire of viruses recognized is expanding with newly found related viruses in different animal species. Direct zoonotic transmission appears to be rare, but genetic mixing of animal and human viruses seems plausible with the finding that common human strains replicate in pigs and cattle. A major finding was the evolutionary mechanism behind the success of the GII4 strains that are dominant in outbreak based surveillance data. The studies in developing countries show that the diversity of viruses involved in these settings is broader.The data described show that the success of noroviruses is determined by an intricate interplay between virus evolution and susceptibility of the host, both genetically and immunologically. The impact of noroviruses as cause of significant illness in children worldwide has been underestimated and needs to be taken seriously. Evidence-based prevention and intervention strategies are urgently needed.