Global waste generation is expected to continue to grow due to economic development and population growth. Therefore, sustainable waste management is mandatory if a sustainable world is desired in which the objectives of the circular economy concept are met, where recovery is the last step to be taken when reduce, reuse or recycle have already been carried out. Waste-to-energy processes could constitute a way to recover energy from waste, helping the access to renewable energy to the world population, in addition to a waste management system. The present review describes different wastes that can be employed in waste-to-energy processes, using thermo-chemical, biochemical and chemical processes. The energy produced can be in the form of heat, electricity or biofuels. For each of these processes, the feedstock used, the state-of-the-art in recent years and the expected trends for the coming years are briefly discussed.