This review article discusses the valorisation of lignin as a resource for chemicals in biorefineries. It highlights three key aspects: (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. These interconnected processes are essential for the successful conversion of lignin into valuable chemicals. The review provides an overview of the extensive research on these topics, ranging from established techniques to cutting-edge innovations. It also outlines strategies to minimize lignin condensation during fractionation and depolymerisation, such as preserving the lignin structure or quenching reactive intermediates. Upgrading depolymerised lignins through convergent transformations, such as funneling, is presented as a promising approach to reduce complexity. The review also discusses the chemical composition of lignocellulose, including cellulose, hemicellulose, and lignin, and their roles in biomass recalcitrance. It covers various lignin chemistry mechanisms, including base-catalysed, acid-catalysed, reductive, oxidative, and thermal processes, and their impact on lignin structure and reactivity. The article also reviews different fractionation methods, such as alkaline and acidic delignification, and their effects on lignin isolation and properties. Finally, it discusses the importance of lignin fractionation in biorefineries and the challenges associated with its valorisation.This review article discusses the valorisation of lignin as a resource for chemicals in biorefineries. It highlights three key aspects: (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. These interconnected processes are essential for the successful conversion of lignin into valuable chemicals. The review provides an overview of the extensive research on these topics, ranging from established techniques to cutting-edge innovations. It also outlines strategies to minimize lignin condensation during fractionation and depolymerisation, such as preserving the lignin structure or quenching reactive intermediates. Upgrading depolymerised lignins through convergent transformations, such as funneling, is presented as a promising approach to reduce complexity. The review also discusses the chemical composition of lignocellulose, including cellulose, hemicellulose, and lignin, and their roles in biomass recalcitrance. It covers various lignin chemistry mechanisms, including base-catalysed, acid-catalysed, reductive, oxidative, and thermal processes, and their impact on lignin structure and reactivity. The article also reviews different fractionation methods, such as alkaline and acidic delignification, and their effects on lignin isolation and properties. Finally, it discusses the importance of lignin fractionation in biorefineries and the challenges associated with its valorisation.