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 primary aim is to unify and harmonize communication on PFASs among the global scientific, regulatory, and industrial communities. The article defines PFASs, classifies them into various families, and recommends common names and acronyms for both the families and their individual members. It also describes the main production processes (electrochemical fluorination and telomerization) and the types of byproducts (isomers and homologues) that can arise. The article highlights the interrelationships between principal PFAS families as industrial, environmental, or metabolic precursors or transformation products of one another, with a particular focus on those PFASs that can be converted into long-chain perfluoroalkyl carboxylic or sulfonic acids, which are currently the focus of regulatory action. The Supplemental Data lists 42 families and subfamilies of PFASs and 268 selected individual compounds, providing recommended names, acronyms, and structural formulas, as well as Chemical Abstracts Service registry numbers.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 primary aim is to unify and harmonize communication on PFASs among the global scientific, regulatory, and industrial communities. The article defines PFASs, classifies them into various families, and recommends common names and acronyms for both the families and their individual members. It also describes the main production processes (electrochemical fluorination and telomerization) and the types of byproducts (isomers and homologues) that can arise. The article highlights the interrelationships between principal PFAS families as industrial, environmental, or metabolic precursors or transformation products of one another, with a particular focus on those PFASs that can be converted into long-chain perfluoroalkyl carboxylic or sulfonic acids, which are currently the focus of regulatory action. The Supplemental Data lists 42 families and subfamilies of PFASs and 268 selected individual compounds, providing recommended names, acronyms, and structural formulas, as well as Chemical Abstracts Service registry numbers.