This article provides an overview of perfluoroalkyl and polyfluoroalkyl substances (PFASs) detected in the environment, wildlife, and humans, and recommends clear, specific, and descriptive terminology, names, and acronyms for PFASs. The goal is to unify and harmonize communication on PFASs by offering terminology for use by the global scientific, regulatory, and industrial communities. The focus is on long-chain perfluoroalkyl acids, substances related to these acids, and substances intended as alternatives to their use. The article defines PFASs, classifies them into families, and recommends common names and acronyms for both families and individual members. It also discusses the production processes of PFASs, such as electrochemical fluorination and telomerization, and the byproducts likely to arise from these processes. The article shows how the principal families of PFASs are interrelated as industrial, environmental, or metabolic precursors or transformation products of one another. It emphasizes the potential of PFASs to be converted into long-chain perfluoroalkyl carboxylic or sulfonic acids, which are currently the focus of regulatory action. The article also provides a brief review of topics useful for understanding the occurrence and relationships between various families of PFASs in the environment. It discusses the manufacturing processes used to produce compounds containing perfluoroalkyl chains, including electrochemical fluorination and telomerization. The article also provides terminology for describing direct and indirect sources of PFASs to the environment. It defines key terms related to PFASs, including perfluoroalkyl and polyfluoroalkyl substances, fluorinated polymers, and chain length terminology. The article also discusses the use of acronyms for acids and their anions, surfactant terminology, and the classification of PFAS families. The article concludes with a discussion of the environmental occurrence and behavior of PFASs, their sources, and their potential for transformation into long-chain perfluoroalkyl acids. The article also provides a comprehensive list of PFAS families and individual compounds, along with recommended names, acronyms, and structural formulas.This article provides an overview of perfluoroalkyl and polyfluoroalkyl substances (PFASs) detected in the environment, wildlife, and humans, and recommends clear, specific, and descriptive terminology, names, and acronyms for PFASs. The goal is to unify and harmonize communication on PFASs by offering terminology for use by the global scientific, regulatory, and industrial communities. The focus is on long-chain perfluoroalkyl acids, substances related to these acids, and substances intended as alternatives to their use. The article defines PFASs, classifies them into families, and recommends common names and acronyms for both families and individual members. It also discusses the production processes of PFASs, such as electrochemical fluorination and telomerization, and the byproducts likely to arise from these processes. The article shows how the principal families of PFASs are interrelated as industrial, environmental, or metabolic precursors or transformation products of one another. It emphasizes the potential of PFASs to be converted into long-chain perfluoroalkyl carboxylic or sulfonic acids, which are currently the focus of regulatory action. The article also provides a brief review of topics useful for understanding the occurrence and relationships between various families of PFASs in the environment. It discusses the manufacturing processes used to produce compounds containing perfluoroalkyl chains, including electrochemical fluorination and telomerization. The article also provides terminology for describing direct and indirect sources of PFASs to the environment. It defines key terms related to PFASs, including perfluoroalkyl and polyfluoroalkyl substances, fluorinated polymers, and chain length terminology. The article also discusses the use of acronyms for acids and their anions, surfactant terminology, and the classification of PFAS families. The article concludes with a discussion of the environmental occurrence and behavior of PFASs, their sources, and their potential for transformation into long-chain perfluoroalkyl acids. The article also provides a comprehensive list of PFAS families and individual compounds, along with recommended names, acronyms, and structural formulas.