Foreign workers or guest workers are people who work in a country other than one of which they are a citizen. Some foreign workers use a guest worker program in a country with more preferred job prospects than in their home country. Guest workers are often either sent or invited to work outside their home country or have acquired a job before leaving their home country, whereas migrant workers often leave their home country without a specific job in prospect.

Tens of millions of people around the world operate as foreign workers. As of 2018, according to reports from the Bureau of Labor Statistics, there is an estimated 28 million foreign-born workers in the United States, which draws most of its immigrants from Mexico, including 4 or 5 million undocumented workers. It is estimated that around 5 million foreign workers live in northwestern Europe, half a million in Japan, and around 5 million in Saudi Arabia. Between January and June in 2019, 2.4 million foreigners arrived to work in Russia. A comparable number of dependents may accompany international workers.

Some foreign workers migrate from former colonies to a former colonial metropole (France, for example).Chain migration may operate in building guest-worker communities.