Pfam is a database of protein families that currently contains 7973 entries (release 18.0). A recent development in Pfam has enabled the grouping of related families into clans. Pfam clans are described in detail, together with the new associated web pages.his represents 15% of Pfam families and as these tend to represent the larger protein families, account for 31% of the domain hits in Pfam. Clans help us to improve the annotation of families. For example, knowing the 3D structure of a domain is an essential part of understanding the biology of that domain.