The Geiger–Müller counter, also called a Geiger counter, is an instrument used for measuring ionizing radiation.
It detects radiation such as alpha particles, beta particles and gamma rays using the ionization produced in a Geiger–Müller tube, which gives its name to the instrument. In wide and prominent use as a hand-held radiation survey instrument, it is perhaps one of the world's best-known radiation instruments.
The original detection principle was discovered in 1908, but it was not until the development of the Geiger-Müller tube in 1928 that the Geiger-Müller counter became a popular instrument for use in such as radiation dosimetry, radiological protection, experimental physics and the nuclear industry. This was mainly due to its robust sensing element and relatively low cost, however there are limitations in measuring high radiation rates and in measuring the energy of incident radiation.