The furnace is the heart of every incineration plant. The selection of the most suitable firing technology depends on the used fuels as well as demands on the plant overall. I focus on solid fuels, such as biomass or waste materials, as well as gaseous and liquid fuels. My references range from grate and fluidized bed firing systems (bubbling fluidized bed (BFB) and circulating fluidized bed (CFB)) to post-combustion chambers for low calorific gases.