The commonly used thermocouple types are identified by letter designations originally assigned by the Instrument Society of America (ISA) and adopted as an American Standard in ANSI MC 96.1. This chapter covers general application data on the atmospheres in which each thermocouple type can be used, recommended temperature ranges, limitations, etc. Physical and thermoelectric properties of the thermoelement materials used in each of these thermocouple types are also presented in this section.