Formation of new actin filaments is essential for cell movement, growth and division. The Arp2/3 complex is a well-established nucleator of actin filaments, but recent work has revealed that there are other players in this game: the formins. In a Commentary on p. 2603, Charles Boone and co-workers discuss work illuminating the roles of these proteins, which can nucleate actin filaments in vitro and are implicated in numerous actin-dependent processes. Formins contain two conserved domains: FH2, which probably mediates filament nucleation; and FH1, which might facilitate delivery of actin monomers to growing filaments by interacting with the G-actin-binding protein profilin. Recent work indicates that regulation of formin activity, in at least some cases, depends on additional, N-terminal sequences; in the case of formins related to the protein Diaphanous, for example, these interact with the small GTPase Rho, allowing the molecules to function as effectors in Rho signalling. Other studies indicate that formins are important for spindle positioning in yeast and modulate microtubule organization in mammalian cells. Indeed these proteins appear to link the microtubule and actin filament systems and thereby help to establish cell polarity.