The incorporation of the biorefinery concept into the pulp and paper industry represents a strategic evolution toward a circular bioeconomy, proposing the full valorization of lignocellulosic biomass. This chapter presents a critical analysis of conventional pulp production processes (e.g., mechanical, sulphite, and kraft methods), highlighting their limitations in terms of selectivity, component recovery, and environmental sustainability. In contrast, the application of emerging pretreatment technologies, such as autohydrolysis, vapor explosion, ionic liquids, and organosolv processes, is explored, capable of promoting the selective fractionation of biomass and expanding the range of products obtained. In this context, emphasis is placed on the production of high-added-value biocomposites, including nanocellulose (crystalline and microfibrillated), second-generation bioethanol, regenerated fibers (such as lyocell), carbon fibers from lignin, vanillin, lignin adhesives, and functional materials with conductive properties. Case studies are presented from leading companies in the sector (e.g., Suzano, Borregaard, Stora Enso, and Lenzing) that have demonstrated the technical and economic viability of biorefinery integration, with a positive impact on portfolio diversification, reducing carbon emissions, and valorizing historically underused by-products. Finally, it can be concluded that the pulp industry’s transition to a multifunctional biorefinery model is a viable way of promoting greater efficiency in the use of biomass, reducing environmental impacts, and making the sector a key player in consolidating the global bioeconomy.