The present Supplement Volume Beryllium A 3 continues and completes the description of the physical properties of the element, begun in Supplement Volume A 2, 1991, and also treats the electrochemical behavior of the metal. The unique combination of the Be properties, which was pointed out in Supplement Volume A 2, is also demonstrated in the following chapters of this Volume A 3: 13. Electrical Properties 14. Electronic Properties 15. Optical Properties. Emission and Impact Phenomena 16. Electrochemical Behavior Starting with the electrical properties, Be isarather good electrical conductor in centrast to what might be expected. Superconductivity was studied, especially on films. Quantum effects, which are more pronounced in Be than in most other metals, are the reason for numerous in­ vestigations of the magnetoresistance and the magnetic-breakdown effect. The basis for many of the characteristic properties is the unique nature of bonding in Be as a consequence of its peculiar electronic structure and the special shape of its Fermi surface which also gave rise to further numerous studies. Detailed cluster calculations were per­ formed to better understand the bonding in the metal. Regarding the optical properties, the high reflectivity of Be, particularly in the infrared region, makes it attractive for the fabrication of precision optical surfaces (mirrors); it is also useful for solar-collector surfaces in spacecraft applications. Emission and electron-and ion­ impact phenomena as well as neutron optics are also discussed.