Diamond is an extreme material among possible atomic aggregations in nature, and as such has many extreme properties. This unique position makes it a fascinating subject both for science and for applications. This has been particularly true in recent years, since the surprising discovery at Union Carbide (1953) of the possibility of chemical vapour deposition of diamond films at low pressures, where diamond is metastable with respect to graphite. This discovery cleared the way to the development of economical deposition techniques that have been obtaining progressively better-quality diamond.