Catalysis plays a major role at mitigating the environmental impact of the chemical industry, drastically cutting its energy and material consumption. For this Perspective, we have chosen C═O reduction in the context of biomass as a benchmark reaction to introduce and illustrate essential aspects of green catalysis. We first covered the most used C═O hydrogenation substrates made from biomass. Then, we looked at alternative energy sources to convective heating, discussed the use of greener solvents and reductants, and listed a few precious metal-free catalytic systems. Finally, we looked at various hydrogen sources, including biosourced ones. In particular, we emphasized the use of metrics in order to quantify the actual impact of these innovations.