The mechanism of spin–phonon coupling (SPC) and possible consequences for the properties of high-TC copper oxides are presented. The results are based on ab initio LMTO band calculations and a nearly free-electron (NFE) model of the band near EF. Many observed properties are compatible with SPC, as for the relation between doping and q for spin excitations and their energy dependence. The main pseudogap is caused by SPC and waves along 100 but it is suggested that secondary waves, generated along 110, contribute to a waterfall structure. Conditions for optimal TC, and the possibilities for spin enhancement at the surface are discussed.