Gold nanocatalysts with different sizes (nanoparticles and nanoclusters) show different catalytic performances for various selective hydrogenation reactions. The recent breakthrough in a controllable synthesis of atomically precise gold nanoclusters provides unprecedented opportunities for understanding the catalytic behavior at the atomic/molecular levels. Herein, we review the progress in catalytic hydrogenation over gold nanoparticles and atomically precise gold nanoclusters in the last five years. We also compare the results obtained from different reactions so that a better understanding of their catalytic behavior can be obtained. Finally, we provide some future perspectives on gold nanocatalysis.