A systematic method is presented to synthesize reactive crystallization processes. It shows how to selectively crystallize a desired solid product(s) after a reaction step and how to use compound formation to effect separation of a mixture. The method is based on the generation of phase diagrams with liquid-phase reactions. Using transformed coordinates, systems with three or fewer degrees of freedom can be conveniently analyzed, regardless of the number of components and reactions. Features of the solid-liquid phase diagram that are relevant to process synthesis are identified. The method is illustrated with systems with multiple components, complex reactions, and multiple phases.