Abstract
Astroviruses and caliciviruses are two families defined initially by their characteristic morphology. Many of these viruses have been difficult to grow in culture. Molecular biology has now provided a valuable insight into the nature of these viruses, and in many respects knowledge of genome structure now outstrips that of more classical virological features. However these advances have allowed a more detailed approach to virus classification and have led to the establishment of the Astroviridae as a distinct virus family.