Biomass (e.g., plant biomass, animal biomass, and municipal waste biomass) is processed to produce useful intermediates and products, such as energy, fuels, foods or materials. For example, compositions and methods are described that can use feedstock materials, such as cellulosic and/or lignocellulosic materials, a cellulase and a second enzyme system including an amylase to produce an intermediate or product, e.g., by fermentation.