This book emphasis on ion selective electrode with calix[4]arene for Neodium (III) and phospahte ions. Concerning its applications, it was effectively employed for the determination of neodymium ions in industrial waste water as well as in lake water. As well as for phosphate ions, the developed sensor was used as an indicator electrode in potentiometric titration of monohydrogen phosphate ion with barium chloride. The proposed sensor was successfully applied for the direct determination of monohydrogen phosphate in real life samples.