The catalytic reduction of carboxylic acid derivatives has witnessed a rapid development in recent years. These reactions, involving molecular hydrogen as the reducing agent, can be promoted by heterogeneous and homogeneous catalysts. The milestone achievements and recent results by both approaches are discussed in this Review. In particular, we focus on the mechanistic aspects of the catalytic hydrogenation and highlight the bifunctional nature of the mechanism that is preferred for supported metal catalysts as well as homogeneous transition metal complexes.