The ability of molecules to crystallize in more than one arrangement in the solid state has profound implications for a variety of phenomena including pigment properties, solid state reactivity, and pharmaceutical performance. We are developing techniques to control the process of crystallization in a general fashion with the goal of making materials with improved functionality.  Our approach exploits polymers as phase directors. Combinatorial materials chemistry plays a vital role in these efforts as do advanced analytical techniques including X-ray microdiffraction, thermal analysis, and Raman spectroscopy.  Design of new polymeric systems for controlling pharmaceutical crystallization and elucidating mechanisms of form selection are topics of current interest.