What we have established by electron paramagnetic resonance (EPR) studies i
n silicon concerning the properties of its intrinsic defects (vacancies and
interstitials) and their interactions with other defects is reviewed. The
lessons learned are compared to what is currently being observed in diamond
, and some general observations made. Also described is a recent identifica
tion by EPR of a dominant electrically active defect involving a single hyd
rogen atom in CVD diamond.