A gas chamber is an apparatus for killing humans or animals with gas, consisting of a sealed chamber into which a poisonous or asphyxiant gas is introduced. The most commonly used poisonous agent is hydrogen cyanide; carbon dioxide and carbon monoxide have also been used. Gas chambers were used as a method of execution for condemned prisoners in the United States beginning in the 1920s. During the Holocaust, large-scale gas chambers designed for mass killing were used by Nazi Germany as part of their genocide program, and also by the Independent State of Croatia at the Jasenovac concentration camp. The use of gas chambers has also been reported in North Korea.

Gas chambers have been used for capital punishment in the United States to execute criminals, especially convicted murderers. The first person to be executed in the United States by lethal gas was Gee Jon, on February 8, 1924. An unsuccessful attempt to pump poison gas directly into his cell at Nevada State Prison led to the development of the first makeshift gas chamber to carry out Gee's death sentence. In 1957, Burton Abbott was executed as the governor of California, Goodwin J. Knight, was on the telephone to stay the execution. Since the restoration of the death penalty in the United States in 1976, eleven executions by gas chamber have been conducted. By the 1980s, reports of suffering during gas chamber executions had led to controversy over the use of this method.