The basic concept of the REFABB project was that by genetically engineering the biomass crop switchgrass to produce a natural polymer PHB, which is readily broken down by heating (thermolysis) into the chemical building block crotonic acid, sufficient additional economic value would be added for the grower and processor to make it an attractive business at small scale. Processes for using thermolysis to upgrade biomass to densified pellets (char) or bio-oil are well known and require low capital investment similar to a corn ethanol facility. Several smaller thermolysis plants would then supply the densified biomass, which is easier to handle and transport to a centralized biorefinery where it would be used as the feedstock. Crotonic acid is not by itself a large volume commodity chemical, however, the project demonstrated that it can be used as a feedstock to produce a number of large volume chemicals including butanol which itself is a biofuel target. In effect the project would try to address three key technology barriers, feedstock logistics, feedstock supply and cost effective biomass conversion. This project adds to our understanding of the potential for future biomass biorefineries in two main areas. The first addressed in Task A was the importance and potential of developing an advanced value added biomass feedstock crop. In this Task several novel genetic engineering technologies were demonstrated for the first time. One important outcome was the identification of three novel genes which when re-introduced into the switchgrass plants had a remarkable impact on increasing the biomass yield based on dramatically increasing photosynthesis. These genes also turned out to be critical to increasing the levels of PHB in switchgrass by enabling the plants to fix carbon fast enough to support both plant growth and higher levels of the polymer. Challenges in the critical objective of Task B, demonstrating conversion of the PHB in biomass to crotonic acid at over 90% yield, demonstrated the need to consider up-front the limitations of trying to adopt existing equipment to a task for which subsequent basic research studies indicated it was not suitable. New information was developed in the most complex of the chemical conversions studied, advanced catalysis to make acrylic acid, a chemical used widely to make paints, and this was published in a scientific journal. In regard to the technical effectiveness, the crop science aspects were for the most part remarkably effective in addressing the underlying objectives indicating the soundness of the technical approach. With time, it should be possible to fully develop the advanced biomass biorefinery feedstock. Challenges within the thermolysis step to recover crotonic acid meant that by the end of the project we were not able to demonstrate an economic case based on data from scaled up equipment. Solving this will take further research and development work. As a general statement, the broadest public good is in demonstrating the value of funding a very unique approach to the complex problem of enabling large-scale biomass biorefineries which resulted in significant progress towards the ultimate goal and a clearer understanding of the technical hurdles remaining. Perhaps not surprisingly, some of the broader benefits to the public come from the use of the REFABB project innovations in areas unrelated to the initial objective. It is worth highlighting the breakthrough developments in identifying three single global regulator genes which can be engineered into plants to dramatically increase photosynthesis and carbon capturing ability. These genes have tremendous potential for use in major food crops, in particular corn to enhance grain yield and based on recent findings, increase the root density, a critical key to increasing carbon sequestration in agriculture and improving the sustainability of global food and biofuel production.