[en] The results of experimental studies of Moessbauer effect on various rare-earth (R) and doping nuclei (M = Sn-119, Fe-57) in RBa2(Cu(1-x) - Mx)3O(7-y) high-temperature superconductors are reviewed. The following major problems connected with the Moessbauer isotopes are revealed: systematization of the observed experimental spectra depending on the parameters (x, y, Tcr, isotropic polycrystals, textured polycrystals, monocrystals); spectral decomposition algorithms; spectral parameters stability with respect to the decomposition algorithm and initial fitting parameters variations; the character of spectral parameter variations versus different variables (x, y, Tcr and oth.); spectra interpretation; extraction of information on HTSC properties from the Moessbauer spectroscopy data. Besides this the character of including Sn and Fe doping nuclei into the crystal matrix is also discussed. 108 refs.; 9 figs.; 13 tabs