A review concerns catalysts based on polymers and compares their advantages and disadvantages with other industrial catalysts. Basic information is given on the preparation of polymer-based catalysts, especially by the functionalization of polymeric materials. Main part of the review presents applications of polymer-based catalysts, e.g., in the production of methyl tert-butyl ether, tert-amyl methyl ether, bisphenol A, acrylic esters, and phenol derivatives, and in the hydration of olefins, etc.