Lignocellulosic biomass, of which brewer’s spent grain (BSG) is a part, has a varied composition and requires various pre-treatments to extract compounds with added value. Pre-treatments bring several advantages: they open the structure of the cell wall, decrease the particle size, reduce cellulose crystallinity, and improve digestibility. Solvent extraction methods, diluted acid methods, alkaline, supercritical carbon dioxide extraction, microwave-assisted extractions, or ultrasonic extractions have as their main objective the change of the crystallinity of lignocellulosic biomass and the detoxification of inhibitors to improve hydrolysis and general saccharification. Pre-treatments are essential strategies that disrupt the structure of the BSG and help remove lignin, thus facilitating the exposure of polysaccharides for optimal extraction efficiency. The complexity and heterogeneity of biomass decide the extraction method used. Efficient, economically feasible, simple extraction methods, from which no inhibitors and no corrosive materials are produced, are taking into account.