Tunneling Systems in Amorphous and Crystalline Solids

1. Introduction.- 2. Heat Release in Solids.- 3. Crossover to Phonon-Assisted Tunneling in Insulators and Metals.- 4. Influence of Tunneling Systems on the Acoustic Properties of Disordered Solids.- 5. Interactions Between Tunneling Defects in Amorphous Solids.- 6. Investigation of Tunneling Dynamics by Optical Hole-Burning Spectroscopy.- 7. Tunneling of H and D in Metals and Semiconductors.- 8. Microscopic View of the Low-Temperature Anomalies in Glasses.- 9. Beyond the Standard Tunneling Model: The Soft-Potential Model.- References.