Biomass has always been a reliable source of energy, from the first manmade fire to the utilization of pelletized wood as a feed for thermal plants. Although the use of lignocellulosic feedstock as a solid biofuel is a well-known concept, conversion of biomass into liquid fuel is a considerable challenge, and the more complex the biomass gets (in terms of chemical composition) the more complicated and generally expensive the conversion process becomes. Depletion of the oil stocks combined with the increasing worldwide energy demand has generated an increased interest toward biofuels in the past 10-20 years, although for most ofthe twentieth century research on biofuel closely followed the price of petroleum. Another growing concern in the past 50 years is the environmental aspects of liquid fuel consumption. With the growing concerns about the greenhouse gas emissions, the use of biofuels, although sometimes criticized, is often a more environmentally friendly option because the carbon balance of biofuel is close to neutral when compared with petroleum-derived fuels such as gasoline, diesel, or kerosene. The "first-generation" biofuels appear unsustainable because of the potential stress that their production places on food commodities. For organic chemicals and materials, these needs to follow a biorefinery model under environmentally sustainable conditions. Where these operate at present, their product range is largely limited to simple materials (i.e., cellulose, ethanol, and biofuels). Second-generation biorefineries need to build on the need for sustainable chemical products through modern and proven green chemical technologies such as bioprocessing including pyrolysis. "Third-generation" algae biofuels and "fourth-generation" biofuels are created using petroleum-like hydroprocessing, advanced biochemistry, or revolutionary processes that defy any other category of biofuels. © Springer International Publishing Switzerland 2015.