The general term metallic glasses is now generally accepted to define a class of amorphous alloys obtained by rapid solidification from the liquid state. This definition corresponds exactly to the definition of a glass in general, except that in the case of well known silicate glasses the liquid does not require a rapid rate of cooling to prevent crystallization, and that is not the case for metallic glasses. The first metallic glass, an alloy of gold and silicon, was synthesized at Caltech in the summer of 1959. During the last 20 years, the interest in metallic glasses has increased steadily. There is still widespread interest in both theoretical and experimental studies of metallic glasses. About 10 years ago the potential importance of metallic glasses as a class of new materials with unusual physical properties was recognized by industry. It will take a long time before production of metallic glasses can be measured in tons, but it is encouraging to see that an increasing number of industrial research centers are involved in studies of metallic glasses.