The experimental procedures for the determination of the most important equilibrium parameters of ion exchangers (ion exchange capacity, ion exchange isotherm, selectivity coefficient, distribution coefficient) are reviewed and discussed. Special emphasis is put on inorganic ion exchangers and ion exchange at trace concentrations. Experimental details that are sensitive for obtaining accurate and reliable equilibrium data are examined. In addition, the effects of physical and chemical phenomena that may distort the results of ion exchange equilibrium studies are examined and some guidelines are given on how to avoid these interferences.