The document provides recommendations for the nomenclature of ion-selective electrodes (ISEs) as part of the International Union of Pure and Applied Chemistry (IUPAC) guidelines. The recommendations aim to standardize the terminology used in the field of electrochemical sensors, particularly those based on potentiometric, amperometric, and conductometric principles. Key definitions and terms are provided, including those for activity, calibration plot, combination electrode, detection limit, interfering substance, ionic-strength or pH adjustment solution, ion-selective electrode (ISE), ISE cell, isopotential point, membrane, membrane sites, Donnan exclusion, Nernstian response, potentiometric selectivity coefficient, range and span, reference electrode, internal reference electrode, response time, standard addition method, standard subtraction method, and the "suspension effect." The document also classifies ISEs into primary, compound/multiple membrane, and metal contact/all-solid-state types, and provides equations for emf responses and definitions of relevant constants. Methods for determining potentiometric selectivity coefficients are outlined, including the fixed interference method (FIM) and separate solution method (SSM).The document provides recommendations for the nomenclature of ion-selective electrodes (ISEs) as part of the International Union of Pure and Applied Chemistry (IUPAC) guidelines. The recommendations aim to standardize the terminology used in the field of electrochemical sensors, particularly those based on potentiometric, amperometric, and conductometric principles. Key definitions and terms are provided, including those for activity, calibration plot, combination electrode, detection limit, interfering substance, ionic-strength or pH adjustment solution, ion-selective electrode (ISE), ISE cell, isopotential point, membrane, membrane sites, Donnan exclusion, Nernstian response, potentiometric selectivity coefficient, range and span, reference electrode, internal reference electrode, response time, standard addition method, standard subtraction method, and the "suspension effect." The document also classifies ISEs into primary, compound/multiple membrane, and metal contact/all-solid-state types, and provides equations for emf responses and definitions of relevant constants. Methods for determining potentiometric selectivity coefficients are outlined, including the fixed interference method (FIM) and separate solution method (SSM).