Laogai (Chinese: 劳改), short for laodong gaizao (劳动改造), which means reform through labor, is a criminal justice system involving the use of penal labor and prison farms in the People's Republic of China (PRC). Láogǎi is different from láojiào, or re-education through labor, which was the abolished administrative detention system for people who were not criminals but had committed minor offenses, and was intended to "reform offenders into law-abiding citizens". Persons who were detained in the laojiao were detained in facilities that were separate from those which comprised the general prison system of the laogai. Both systems, however, were based on penal labor.

Some writers have likened the laogai to slavery.

During the 1950s and 1960s, Chinese prisons, which were similar to organized factories, contained large numbers of people who were considered too critical of the government or "counter-revolutionaries". However, many people arrested for political or religious reasons were released in the late 1970s at the start of the Deng Xiaoping reforms (known as reform and opening).

In the 21st century, critics have said that Chinese prisons produce products for sale in foreign countries, with the profits going to the PRC government. Products include everything from green tea to industrial engines to coal dug from mines. According to James D. Seymour and Richard Anderson, who both teach at Chinese schools, the products made in laogai camps comprise an insignificant amount of mainland China's export output and gross domestic product. They argue that the use of prison labor for manufacturing is not in itself a violation of human rights, and that most prisoners in Chinese prisons are serving time for what are generally regarded as crimes in the West. The West's criticism of the laogai is based not only on the export of products made by forced labor, but also on the claims of detainees being held for political or religious violations, such as leadership of unregistered Chinese House Churches.

Structural changes following the introduction of market reforms have reduced tax revenue to local governments, increasing pressure for local governments to supplement their income from elsewhere. At the same time, prisoners usually do not make a good workforce. The products manufactured by prison labor in China are of low quality and have become unsalable on the open market in competition with products made by non-imprisoned paid labor.

In 1994 the laogai camps were renamed "prisons". However, Chinese criminal law still stipulates that prisoners able to work shall "accept education and reform through labor". The existence of an extensive network of forced-labor camps producing consumer goods for export to Europe and the United States became classified. Publication of information about China's prison system by Al Jazeera English resulted in its expulsion from China on May 7, 2012.

In 2003, the word "laogai" entered the Oxford English Dictionary. It entered the German Duden in 2005, and French and Italian dictionaries in 2006.

Harry Wu has written books, including Troublemaker and Laogai, that describe the system from the 1950s to the 1990s. Wu spent 19 years, from 1960 to 1979, as a prisoner in these camps, for having criticized the government while he was a young college student. After almost starving to death in the camps, he eventually moved to the United States as a visiting scholar in 1985. In 1992, Wu created the Laogai Research Foundation, a human rights NGO located in Washington, DC. In 2008, Wu opened the Laogai Museum in Washington, D.C., calling it the first ever United States museum to directly address human rights in China. In 2008, the Laogai Research Foundation estimated that approximately 1,045 laogai facilities were operating in China, and contained an estimated 500,000 to 2 million detainees.