Microbial fuel cells (MFCs) represent a new method for sustainable bioenergy production and waste organic matter degradation. Electrochemically active bacteria can oxidize organic matter and transfer electrons to the electrode (anode) surface. These electrons flow through an external circuit to the counter electrode (cathode) where oxygen accepts the electrons to form water. At Penn State, we have shown that MFCs can be used to produce electricity from virtually any biodegradable organic matter, from pure carbohydrates to domestic wastewater and treated agricultural residues (i.e. corn stover hydrolysates). With domestic wastewater as the substrate, we can produce up to 500 mW/m2 while at the same time reducing the organic concentration to an acceptable level. Using glucose, we can produce up to 2400 mW/m2 (based on the cathode surface area). Modifying the MFC by removing oxygen from the cathode, and adding a small voltage to the circuit, it is also possible to produce hydrogen gas instead of electricity. For example, we can produce 2.9 moles of hydrogen per mole of acetate (vs a theoretical yield of 4 mol/mol). These findings show that it is possible to recover bioenergy in the form of electricity or hydrogen from a wide range of wastewaters and other biodegradable materials. Further development of these technologies could lead to wastewater treatment processes that are net energy producers rather than consumers.