  The reversal of the magnetization of crystals of molecular magnets that have
a large spin and high anisotropy barrier generally proceeds below the blocking
temperature by quantum tunneling. This is manifested as a series of controlled
steps in the hysteresis loops at resonant values of the magnetic field where
energy levels on opposite sides of the barrier cross. An abrupt reversal of the
magnetic moment of the entire crystal can occur instead by a process commonly
referred to as a magnetic avalanche, where the molecular spins reverse along a
deflagration front that travels through the sample at subsonic speed. In this
chapter, we review experimental results obtained to date for magnetic
deflagration in molecular nanomagnets.
