Hemicellulose and cellulose represent a large potential renewable reservoir of sugars that could be converted into useful fuels and chemicals. Many pretreatment techniques have been developed that allow near complete conversion of hemicellulose and cellulose into their component sugars; however, the harsh conditions required by these techniques can cause the formation of harmful byproducts that inhibit subsequent biologically-based conversions to fuels and chemicals. There is potential for the application of extremophilic hemicellulose- and cellulose-degrading enzymes to reduce the severity of pretreatments and reduce or eliminate these limitations. Of particular value could be heat and acid stable hemicellulase and cellulase enzymes. We screened numerous organisms from Yellowstone National Park and various culture collections for the ability to produce these enzymes at both high temperatures and low pH. One organism tested, Alicyclobacillus acidocaldarius, produced both extracellular hemicellulase and cellulase activities. Our initial characterization studies determined that both the cellulases and hemicellulases were active from 20-90ºC, with the cellulases active over pHs from 2-6 and the hemicellulases active from pH 1-5. Data on the stability and kinetics of these enzymes at elevated temperatures and acidic pHs will also be presented.