Two families of organocatalytically active polystyrene-based copolymers with tunable incorporations of 4-hydroxyproline have been synthesized using two different controlled radical polymerization technologies: nitroxide-mediated polymerization (NMP) and reversible addition−fragmentation chain transfer (RAFT) polymerization. Both of these methodologies allow ready access to a number of polymeric species with controllable molecular weights, narrow molecular weight distributions (ca. 1.2), and reliable functionality incorporations (between 3 and 26%). The organocatalytic activity and selectivity of the NMP-derived family of copolymers with variable incorporations of l-proline have been investigated using the aldol reaction, which provided high conversion to products (>95%) with very good diastereo- and enantioselectivities. We propose that these materials have potential as highly efficient recoverable organocatalyst supports whose solubility and loading can be readily tailored to the desired application.