This chapter examines lignin recovery from black liquor, a byproduct of the pulp and paper industry, emphasizing its role in sustainability and the circular economy. Lignin, an abundant biopolymer, offers potential to replace fossil-based materials in applications such as bioplastics, resins, and construction additives. Despite its value, most lignin is currently burned or discarded, representing a significant waste of resources. The chapter discusses the variable composition of black liquor, influenced by feedstock and pulping conditions, and the challenges in lignin recovery, including structural complexity and high ionic strength. Various recovery methods are reviewed: acid precipitation, membrane filtrations processes, solvent extraction, and thermal processes, each with distinct advantages and limitations. A bibliometric analysis highlights growing research interest, with advancements in purification techniques and industrial applications. Membrane filtration, in particular, stands out for its energy efficiency and ability to preserve lignin integrity, though challenges such as fouling and chemical stability remain. In conclusion, lignin recovery from black liquor is crucial for reducing environmental impact and valorizing industrial waste. The chapter underscores the need for integrated research and optimized processes to develop scalable, sustainable solutions aligned with global decarbonization and resource efficiency goals. Future efforts should focus on overcoming technical barriers and fostering industry-academia collaboration to maximize lignin potential.