The caliciviruses are by far the major cause of non-bacterial gastroenteritis, highly infectious, and have a rapid and severe onset of symptoms. Studies on this family of viruses have been hampered by the lack of animal model and tissue culture system. However, recent advances in protein expression systems and the development of a mouse norovirus animal model has led to rapid advances in our understanding of these viruses with regard to structure and the host immune response. Our current understanding of this important family of viruses is reviewed here.