  Historical review on the studies of the electron paramagnetic resonance in
superconductors performed in the period from 1970 to 1990 at the Kazan Physical
Technical Institute of the Russian Academy of Sciences (group of Dr. E. G.
Kharakhash'yan) in collaboration with Kazan State University (group of Prof. B.
I. Kochelaev) and with the Institute for Physical Problems of Russian Academy
of Sciences (group of Prof. N. E. Alekseevskii) is presented. We have observed
for first time electron paramagnetic resonance of impurities in a type II
superconductor; found indication for a long-range exchange interaction between
magnetic impurities arising due to the superconducting correlations; observed
the magnetic ordering of impurities in the superconducting state; and, finally,
we found one of the first evidences for heterogeneity of the 1:2:3 high-$T_c$
superconductor which is its natural property
