A number of years have elapsed since the last comprehensive review of the chemical properties of carbonyl sulfide (COS) was presented in 1957. Since that time, some important new issues have arisen regarding this fluid. The presence of COS in industrial product streams has always been an important consideration for chemical engineers. An example of a relatively new industrial issue is the presence of naturally occurring COS in liquefied petroleum gas (LPG). It is believed that the hydrolysis of this COS is the cause of corrosion and compliance-testing failures in the LPG industry. New applications of COS have arisen in recent years, such as its use as an agricultural fumigant. Environmental issues also have become more of a concern recently. These issues, as well as many other chemical and physical property issues in science and industry, make this an appropriate time to revisit the chemistry of this interesting fluid, paying special attention to recent observations. In this review, we treat the chemical preparation of COS, its major physical properties, and its major chemical reactions, and then we discuss engineering consequences, applications, and environmental issues.