  We investigate in the framework of linear response theory the complete phonon
dispersion, phonon induced electronic charge response, electron-phonon
interaction and dielectric and infrared properties of the high-temperature
superconductors (HTSC's). In particular the experimentally observed strong
renormalization of the in-plane oxygen bond-stretching modes (OBSM) which
appear upon doping in the HTSC's is discussed. It is shown that the
characteristic softening, indicating a strong EPI, is most likely a generic
effect of the CuO plane and is driven by a nonlocal coupling of the displaced
ions to the localized charge-fluctuations (CF's) at the Cu and O ions. The
different behaviour of the OBSM during the insulator-metal transition via the
underdoped phase is calculated and from a comparison of these modes conclusions
about the electronic state in the HTSC's are drawn. The underdoped state is
modelled in terms of a charge response which is insulator-like at the Cu and is
competing with a metallic charge response at the O-network in the CuO plane.
For the non-cuprate HTSC Ba-Bi-O also a strong renormalization of the OBSM is
predicted. C-axis polarized infrared and Raman-active modes of the HTSC's are
calculated in terms of CF's and anisotropic dipole-fluctuations and the problem
of a metallic character of the BiO planes is studied.Interlayer phonons and
their accompanying charge response are investigated. Depending on the
interlayer coupling calculations are performed from the static, adiabatic- to
the non-adiabatic regime.It is shown that phonon-plasmon mixing and a strong
long-ranged non-adiabatic EPI becomes evident within a certain region around
the c-axis. Both the OBSM and the non-adiabatic coupled c-axis phonon-plasmon
modes are found to be important for pairing in the HTSC's.
