Biomolecular condensates are two- and three-dimensional compartments in eukaryotic cells that concentrate specific collections of proteins and nucleic acids without an encapsulating membrane. Many condensates behave as dynamic liquids, and are believed to form through liquid-liquid phase separation (LLPS) driven by interactions between multivalent constituents. Unlike macromolecular machines such as the ribosome, which have discrete subunit stoichiometries and size, condensates can form with a wide range of component stoichiometries, and range in size from hundreds to thousands of nanometers. While the physical mechanisms that promote and regulate LLPS in vitro and in cells are increasingly well understood, the functions that arise from organization of macromolecules into these meso-scale assemblies remain largely unknown. In my talk I will discuss two related condensates that are both formed by actin-regulatory signaling molecules. I will explain how the molecules assemble into condensates, how this assembly leads to new biochemical and cellular functions, and how these functions are controlled by condensate composition. We believe that our findings have general implications for the function and regulation of biomolecular condensates.