The Kyropoulos method, or Kyropoulos technique, is a method of bulk crystal growth used to obtain single crystals. It is named for , who proposed the technique in 1926 as a method to grow brittle alkali halide and alkali earth metal crystals for precision optics. The largest application of the Kyropoulos method is to grow large boules of single crystal sapphire used to produce substrates for the manufacture gallium nitride-based LEDs, and as a durable optical material.