© The Royal Society of Chemistry 2019.The annual production of fresh tomatoes amounted to approximately 170 million tons in 2017, of which a quarter were grown for the processing industry to produce tomato juice, paste, purée, ketchup, canned tomatoes, and other products. As tomato consumption increases, the quantity of waste and by-products from the tomato processing industry is becoming a critical ecological and financial problem. In the production of tomatoes for ketchup, sauces, or juices, large quantities of residues are generated, accounting for 3.0-7.0% of the total raw materials. Several bioactive compounds can be recovered from these residues, but a significant percentage of them are left unexploited. For this reason it the use of these residues as energy sources, using physical, chemical, and biological technologies, has been proposed. This chapter gives an overall view of the main characteristics of these residues and the possibilities for their conversion into energy.