Members of the actin family have well-characterized cytoskeletal functions, but actin and actin-related proteins (ARPs) have also been implicated in nuclear activities. Previous analyses of the actin family have identified four conserved subfamilies, but many actin-related proteins (ARPs) do not fall into these groups. A new systematic phylogenetic analysis reveals that at least eight ARP subfamilies are conserved from humans to yeast, indicating that these ARPs are part of the core set of eukaryotic proteins. Members of at least three subfamilies appear to be involved in chromatin remodeling, suggesting that ARPs play ancient, fundamental roles in this nuclear process.