Actin-related proteins (ARPs) constitute a family of divergent and evolutionarily ancient eukaryotic proteins whose primary sequences display homology to conventional actins. Whereas actins play well-characterized cytoskeletal roles, the ARPs are implicated in various cellular functions in both the cytoplasm and in the nucleus. Cytoplasmic ARPs, for example, are known to participate in the assembly of branched actin filaments and dynein-mediated movement of vesicles in many eukaryotes. Nuclear ARPs, by contrast, are enigmatic components of various chromatin-modifying complexes involved in transcriptional regulation. Here, we review homologs to several known classes of ARPs and two distinct ARP classes in plants, and summarize recent work elucidating the biological functions of ARPs in eukaryotes.