The attributes and design of soluble polymer supports for catalysis and synthesis are discussed. By manipulating polymer structure, polymer supports can be prepared so that the solubility of an attached reagent. substrate, or ligand is affected by heating, cooling, pH, or solvent identity. Supports with such engineered solubility are useful both in organic synthesis and catalysis. They can be used as purification handles in organic synthesis as a way to recover catalysts, as a way to turn reactions on or off. and more generally. as a handle for separations.