The disclosure provides thermostable enzymes isolated from Caldicellulosiruptor bescii and fragments thereof useful for the degradation of cellulose and/or hemicellulose, including thermostable cellulases and hemicellulases. The disclosure further provides nucleic acids encoding the thermostable enzymes of the disclosure. The disclosure also provides methods for the conversion of cellulose and hemicellulose into fermentable sugars using thermostable enzymes of the disclosure. The disclosure also provides enzyme cocktails containing multiple enzymes disclosed herein. The enzymes can be used to release sugars present in cellulose or hemicellulose for subsequent fermentation to produce value-added products.