Aspects of strong electron-phonon coupling relating to the CDW transition and temperatures above it.

A review of the strong-coupling theory for charge density wave transitions is presented. It is argued that for strong electron- phonon coupling Migdal's theorem is invalid in a wide temperature range above transition. The quasiparticle picture then breaks down. This is possibly the reason for the well known elastic, magnetic and conductivity anomalies in transition metals and compounds.