Lignin, traditionally considered a low-value byproduct of the pulp and paper industry, has gained significant attention in recent years as a sustainable precursor for the development of functional materials. This paradigm shift is driven by recent studies exploring the structure–property–performance relationships of lignin-based functional materials, which have provided valuable insights for selective chemical functionalization or pretreatment of lignin. Furthermore, the use of complementary analytical techniques has helped to shed light into lignin’s complex and heterogeneous structure, opening new avenues for chemical modification. Finally, the emergence of colloidal lignin nanoparticles (LNPs) over the past decade has significantly contributed to the advancement and potential applications of lignin-based functional materials in diverse fields, including drug delivery and complex supramolecular systems.