Fractionating lignocellulosic biomass efficiently is far from being a mundane or trivial task. Within plant biomass (lignocellulose) there are several components (cellulose, hemicellulose and lignin), each of which carries their own requirements for dissolution. To enable a holistic valorization of biomass, those components should be fractionated to individual streams of cellulose, hemicellulose and lignin to allow for a separate downstream processing of them for the production a range of green chemicals, energy and materials. Towards this direction, our aim within FLEXI-GREEN FUELS was to develop an organosolv fractionation process that will enable the extraction of lignin and hemicellulose, leaving behind a cellulosic pulp. Prior to any efficient component extraction there are linkages and connections between the major biomass structures requiring cleavage before one can take advantage of specific solvent-component extraction. Within the FLEXI-GREEN FUELS project, LTU has studied both aspects of the extraction processes through organosolv fractionation on two different lignocellulosic materials, namely wheat straw and beechwood sawdust. To optimize the organosolv fractionation we studied the effect of several process parameters, such as temperature, time, catalyst contents, solvent composition. Throughout the time of this project, the results not only suggest that beechwood and wheat straw can be efficiently fractionated, but also provides additional details on how the process can be affected through for example solvent compositional changes. The influence of the fractionation process is obviously visible through characterization parameters such as delignification and pulp composition, and mitigates further through specific lignin chemical characteristics such as motif distribution and molecular weights, and eventually connects to the distribution and characteristics of the other two major biomass components, namely the hemicellulose and cellulose. Concluding the results obtained thus far – organosolv fractionation has proved to be an efficient method for fractionation of lignocellulosic biomass, yielding pure cellulose pulps, high lignin extraction efficiencies, and an aqueous product with a high content of the hemicellulose fraction