Actin filament assembly occurs in all eukaryotic cells and involves a delicate balance between factors that promote assembly and factors that inhibit assembly. Filament assembly begins with a process of nucleation and then proceeds via elongation. Filament assembly in vivo requires nucleation and elongation factors to overcome barriers that could either bind actin monomers to inhibit nucleation or “cap” the ends of elongating filaments. The formation of most cellular actin structures depends on two or more such factors, which may interact directly. The interaction between two factors that initiate nucleation and promote assembly has recently been demonstrated by Dennis Breitsprecher, Richa Jaiswal, Jeffrey Bombardier, Christopher Gould, Jeff Gelles, and Bruce Goode. Interestingly, the model of these factors in action (Figure 1) resembles a rocket launcher!