Caliciviridae is split into four genera, vesivirus and lagovirus contain animal calicivirus while Norwalk-like virus and Sapporo-like virus pertain to humans.

The Norwalk-like viruses, also known as small round structured viruses, are divided into two subgroups: genogroup I and genogroup II. Genogroup I contains Norwalk virus, Desert Shield, and Southhampton. Genogroup II contains Lordsdale virus, Camberwell virus, Toronto virus, Mexico virus, Bristol virus, Snow Mountain virus, Melksham virus, and Hawaii virus.

Genogroups I and II share various characteristics of morphology. Both groups appear to be round with ragged outlines. The capsid is icosahedral with a triangulation number of 3. The capsid contains 90 dimers and 32 surface depressions that occur at the 5 and 3 fold axes. Neither genogroup can be grown in culture and attempts to infect animals have not yet led to an animal model. Both groups contain three open reading frames: the first encodes a nonstructural polyprotein, the second encodes capsid structural protein, and the third encodes basic protein. One difference in the genogroups is that the first genogroup has a larger genome of 7.7 kb while the second's genome is 7.5 kb. There is also a difference in the overlap of open reading frame 1 and open reading frame 2; the overlap of genegroup 1 includes 17 nucleotides while the overlap of genogroup 2 is 20 nucleotides long.