  The main part of this review is devoted to the comprehensive description of
coherent radiation by nuclear spins. The theory of nuclear spin superradiance
is developed and the experimental observations of this phenomenon are
considered. The intriguing problem of how coherence develops from initially
incoherent quantum fluctuations is analysed. All main types of coherent
radiation by nuclear spins are discussed, which are: free nuclear induction,
collective induction, maser generation, pure superradiance, triggered
superradiance, pulsing superradiance, punctuated superradiance, and induced
emission. The influence of electron-nuclear hyperfine interactions and the role
of magnetic anisotropy are studied. Conditions for realizing spin superradiance
by magnetic molecules are investigated. The possibility of nuclear matter
lasing, accompanied by pion or dibaryon radiation, is briefly touched.
