Owing to the robust chemical attributes, per- and polyfluoroalkyl substances (PFAS) were indiscriminately utilized in various sectors of the industry. However, citing environmental and human health risks, numerous types of PFAS have been gradually phased out by manufacturers. These synthetic chemicals are highly persistent in the environment. As worldwide regulation is becoming stricter for longer-chain perfluorooctanoic acid (PFOA) and perfluorooctane sulphonate (PFOS), the alternative of shorter chains and emerging PFAS have gained global attention. In this chapter, the phasing out of legacy PFAS has been thoroughly discussed along with the physicochemical properties of PFAS. Additionally, the fate and transportation mechanism of PFAS in the environment is also demonstrated. Special focus was given to the impacts of legacy PFAS on the environment and human health. Moreover, the role of short-chain PFAS chemicals as alternatives was also discussed. The book chapter highlights the PFAS pathways and bioaccumulation in aquatic systems and provides a reference for future research and development.