The current production and linear consumption model that ends in disposal needs to be urgently rethought given the huge amount of waste generated in a wide range of industrial processes. There are possible solutions, such as reintroducing these residues back into the production chains, based on the circular economy model as they can be valuable sources of interesting compounds, such as proteins – the primary constituents of living beings. Combining urgent issues such as the increasing scarcity of natural resources; a large amount of food and waste by-products; an increase in the human population expected in the coming years; and the problem of hunger and malnutrition affecting millions of people, new sources of protein directed to human nutrition – as well as animal and other human applications – must be developed, in addition to conventional (meat from livestock) and even alternative sources (plant-based protein, from crops). Considering this scenario, this chapter aims at discussing the processes to obtain proteins from food waste, and analyzing conventional and novel protein extraction methods. Thus, obtaining proteins from food waste, a major residue stream with high chemical potential that is currently being used for low-value applications, could promote an even greener and more sustainable food chain.