Transforming the petroleum-based polymer industry into a sustainable industry has been a major focus of research and industrial sectors for decades. Since 1845, after the first synthesis of poly(lactic acid) (PLA) by Theophile-Jules Pelouze, it emerged as a highly promising bio-based polymer. Since then, synthesis mechanisms have been developed to optimize material properties, and research continues to expand its applications. The ring-opening polymerization of lactide enables tuning of the molecular weight, crystallinity, and stereochemical arrangement in PLA. Current advances rely on PLA green chemistry, allowing wider innovations. Functionalization of lactic acid and the use of organocatalytic and enzyme-mediated systems have enhanced the green chemistry profile of PLA. In addition, advancements in copolymerization, reactive blending, and nanofiller integration also broaden applicability, addressing limitations of commercially available PLA grades. The use of PLA is prominent in biomedical applications; it is widely used in agriculture and in the packaging industry. However, optimizing the properties of PLA and achieving effective decomposition under mild conditions remain critical challenges. This chapter provides an analysis of synthesis mechanisms, material characteristics, recent advancements in molecular design and applications, while exploring future implications of PLA as a potential material for building a sustainable pathway to a circular economy.