Papillomaviruses are highly diverse, and likely occur in
most mammals and birds. Hundreds of ‘‘PV types’’ have
been detected in humans, the only intensively studied host.
It took three decades of research of a large number of
specialists and sequences from thousands of PV isolates to
establish a database that allows us to propose a classification
system that will likely be stable while more PV types
will be found. Here we review this database and its
interpretation by phylogenetic criteria that led to the
taxonomic levels ‘‘family’’, ‘‘genus’’, ‘‘species’’, ‘‘types’’,
‘‘subtypes’’, and ‘‘variants’’.