This review gathers information on the possible ways to valorise Brewer's Spent Grain with an emphasis on building block obtention for polymer synthesis as well as its use as natural filler. The advantages of such a bioresource are its low price, high availability throughout the year and variable and tuneable composition of the fractions of interest depending on malt type. Finally, another advantage of BSG is its soft matrix found to be the easiest to fractionate compared to other biomasses: milder conditions and shorter reaction time are needed resulting in greener valorisation pathways. However, BSG is rapidly perishable due to its high MC, leading to an expensive drying step with high environmental impact. Also, its soft matrix leads to a higher sensitivity to degradation, especially for carbohydrates fractions that can be degraded in furan derivates and humines.