By adjusting the concentrations of ligands—non-scaffold molecules that bind to particular sites on scaffolds—phase transitions of scaffolds can be controlled. The valence of ligands, whether or not they bind directly to stickers or spacers, and the relative affinities of ligand-scaffold versus scaffold-scaffold interactions determine the modulatory effects of ligands. The concentration of scaffolds in condensates is typically diluted by all ligands. Multivalent ligands can stabilise condensates by binding directly to spacers or destabilise condensates by binding directly to stickers, in contrast to monovalent ligands, which destabilise condensates. Even when they have no effect on condensate stability, bipartite ligands that bind to stickers and spacers can change the structural arrangement of scaffold molecules there.