Conventional resources mainly fossil fuels are becoming limited because of the rapid increase in energy demand. This imbalance in energy demand and supply has placed immense pressure not only on consumer prices but also on the environment, prompting mankind to look for sustainable energy resources. Biomass is one such environmentally friendly renewable resource from which various useful chemicals and fuels can be produced. A system similar to a petroleum refinery is required to produce fuels and useful chemicals from biomass and is known as a biorefinery. Biorefineries have been categorized in three phases based on the flexibility of input, processing capabilities, and product generation. Phase I has less or no flexibility in any of the three aforementioned categories. Phase II, while having fixed input and processing capabilities, allows flexibility in product generation. Phase III allows flexibility in all the three processes and is based on the concept of high- value low- volume ( HVLV) and low- value high-volume ( LVHV) outputs. This paper reviews the concept of biorefinery, its types, future directions, and associated technical challenges. An approach of streamlining biorefineries with conventional refineries in producing conventional fuels is also presented. Furthermore, twelve platform chemicals that could be major outputs from an integrated biorefinery are also discussed.