The results of theoretical studies on the spin excitations of the exte
nded t - J model treated in the slave-boson mean field theory are brie
fly summarized and compared with the experimental results of neutron s
cattering and nuclear magnetic resonance both for LSCO and YBCO. It is
found that there exists reasonable overall agreement between experime
nts and the theory, which predicts the dx2-y2 superconductivity. The r
emaining unresolved questions are identified and the possible resoluti
ons for some of these are proposed.