This review describes the synthetic routes to various types of organic polymeric monoliths. Significant concentration is applied to the role of these continuous, porous structures in both heterogeneous catalysis and biocatalysis. A monolith is composed of a solitary mass filled with interconnected pores, which include both large flow-through pores and smaller meso- or micropores. These porous monolithic materials have several advantages over conventional packed beds of porous polymeric beads, owing to their macroporosity and lack of interstitial spacing. Their large pores contribute to mass transfer, which allows the structure to withstand higher back pressures than conventional packed beds, whereas their small pores still operate by diffusion. The effect of multiple parameters, such as the temperature, the cross-link density, and the type and content of porogenic solvent on the pore formation and pore size distribution is outlined for monoliths prepared through free radical polymerization and ring-opening metathesis polymerization (ROMP). Post-functionalization of these monoliths to control the surface chemistry of the supports and/or affix functional catalysts is elucidated, as well as employment of these supports in continuous catalytic reactions. Significant advances in supported catalysis for metathesis, Heck, Suzuki, Sonogashira–Hagihara, and biocatalytic reactions are described.