  The Thick Gas Electron Multiplier (THGEM) is a robust high-gain gas-avalanche
electron multiplier - a building block of a variety of radiation detectors. It
can be manufactured economically by standard printed-circuit drilling and
etching technology. We present a detailed review of the THGEM and its
derivatives. We focus on the physics phenomena that govern their operation and
performances under different operation conditions. Technological aspects
associated with the production of these detectors and their current and
potential applications are discussed.
