  Low counting experiments (search for double $\beta$ decay and dark matter
particles, measurements of neutrino fluxes from different sources, search for
hypothetical nuclear and subnuclear processes, low background $\alpha$,
$\beta$, $\gamma$ spectrometry) require extremely low background of a detector.
Scintillators are widely used to search for rare events both as conventional
scintillation detectors and as cryogenic scintillating bolometers. Radioactive
contamination of a scintillation material plays a key role to reach low level
of background. Origin and nature of radioactive contamination of scintillators,
experimental methods and results are reviewed. A programme to develop radiopure
crystal scintillators for low counting experiments is discussed briefly.
