A biorefinery can be considered as the optimized performance of the use of biomass for materials, chemicals and energy applications. Fast pyrolysis of biomass as the core of a system to optimize the use of biomass is examined. The characteristics and advantages of pyrolysis forming the core of a biorefinery are summarized. Some scenarios in which the unique features of fast pyrolysis can be effectively exploited are outlined. Consideration is given to concepts based only on pyrolysis and pyrolysis products; concepts that broaden the scope to encompass other downstream processes; and concepts in which pyrolysis can make a valuable contribution within the broader context of utilization of biomass. This is an abstract of a paper presented at the 230th ACS National Meeting (Washington, DC 8/28/2005-9/1/2005).