This review considers for the first time the effects in heterogeneous catalysis of grain boundaries ( GB) created as a result of consolidation of catalytic materials nanoparticles without their sintering. Different methods proposed for quantitative characterization of nanoparticles consolidation extent were considered together with theoretical basis for increasing of catalytic activity at the GB surface areas between consolidated nanocrystals of metals and metal oxides. The review systemizes the GB effects observed in different areas of heterogeneous catalysis implementing metallic and oxide catalysts with acidic, basic, and redox surface functionality. The review analyzed experimental data that demonstrated the fine details of the structure of GB's. Their contribution to improving the performance of catalytic materials should be accounted for in development of novel catalysts and deeper understanding of catalysts functioning.