This IUPAC Technical Report, authored by a team of experts from various institutions, provides a comprehensive review of electrokinetic phenomena and their measurement and interpretation. The report covers the latest advancements and practical guidelines for performing electrokinetic measurements, with a focus on interpreting results in terms of well-defined quantities, particularly the ζ-potential. The ζ-potential is a key property of charged interfaces, but it is often not the only parameter characterizing the electrical state of the interfacial region; the excess conductivity of the stagnant layer is another important parameter. The report discusses the basic theories and their application ranges, detailed descriptions of main electrokinetic methods, and the validity of underlying theoretical models. It also proposes electrokinetic consistency tests to assess the validity of obtained ζ-potentials. The recommendations are primarily applicable to smooth and homogeneous solid particles and plugs in aqueous systems, with some attention given to nonaqueous media and less ideal surfaces. The report aims to serve as a valuable resource for researchers and practitioners in the field of electrokinetics.This IUPAC Technical Report, authored by a team of experts from various institutions, provides a comprehensive review of electrokinetic phenomena and their measurement and interpretation. The report covers the latest advancements and practical guidelines for performing electrokinetic measurements, with a focus on interpreting results in terms of well-defined quantities, particularly the ζ-potential. The ζ-potential is a key property of charged interfaces, but it is often not the only parameter characterizing the electrical state of the interfacial region; the excess conductivity of the stagnant layer is another important parameter. The report discusses the basic theories and their application ranges, detailed descriptions of main electrokinetic methods, and the validity of underlying theoretical models. It also proposes electrokinetic consistency tests to assess the validity of obtained ζ-potentials. The recommendations are primarily applicable to smooth and homogeneous solid particles and plugs in aqueous systems, with some attention given to nonaqueous media and less ideal surfaces. The report aims to serve as a valuable resource for researchers and practitioners in the field of electrokinetics.