Electrochemical methods are used for metal ion speciation due to their unique advantages. These techniques are unique, as they are based on interfacial phenomena. Electrochemical methods follow the low-energy excitation principle and, hence, are species selective in nature rather than element selective. This chapter discusses state-of-the-art metal ion speciation analysis by electro- and radiochemical methods. The electrochemical methods are useful for the speciation of metals, nonmetals, and organic compounds. The most important metal ions studied for their speciation are silver, arsenic, bismuth, cadmium, cobalt, chromium, copper, euradium, iron, gallium, indium, manganese, molybdenum, nickel, lead, antimony, selenium, tin, tellurium, uranium, vanadium, ytterbium, tungsten, and zinc. Anodic stripping voltammetry is the most widely used electrochemical technique for metal ion speciation in water samples. Isotopic dilution analysis was applied to inorganic mass spectrometry for metal ion speciation. Electrochemical methods are good detection techniques for metal ions, but the speciation of metal ions required the conversion of one form into another.