Foreign workers have been a key element in Saudi Arabia's economy since the earliest days of the state's 71-year existence.
12,000 Americans live in Riyadh
Economic development in the oil-rich country was led by the US oil majors. And oil revenue channelled to the Saudi Government was ploughed into huge development projects masterminded by foreign contractors, using large foreign workforces.
Today, there are many fewer US and European workers in Saudi Arabia than during the oil boom years of the 1970s and early 1980s.
The Saudi Government has less money and less need for landmark projects, some key industries - such as oil exploration and production - have been nationalised and the local workforce has developed to the point where the country needs foreign capital and expertise rather than foreign workers.
But there are still more than five million expatriate workers in a country with a population of about 24 million.
And Saudi Arabia has such a young population - 45% are under 15 - that foreign workers make up more than half of the total workforce, according to some estimates.
The government's stated aim is to reduce the total number of foreigners in the country to less than 20% of the population within 10 years.
Most of today's foreign workers come from the Asian subcontinent, the Philippines and other Arab countries. Many of these people are employed in unskilled jobs traditionally shunned by Saudis.
There are also tens of thousands of Americans and Europeans.
There are 40,000-45,000 US citizens in Saudi Arabia, of whom about two-thirds are workers, the US embassy in Riyadh says.
The biggest employers are in oil, finance and trading.
Saudi Aramco - the formerly US-owned national oil company - is by far the biggest individual employer of Americans. The company has about 2,000 US workers, based mostly in and around the Eastern Province oil town of Dhahran.
About 12,000 Americans live in Riyadh, the Saudi capital, where the bombings took place.
They are split in small numbers among a large range of employers - some working in Saudi-owned businesses and others in companies such as Saudi American Bank where the element of US ownership is much more conspicuous.
The UK embassy in Riyadh says about 30,000 British nationals live in Saudi Arabia, working in all sectors of the economy.
The biggest single employer of Britons - with about 2,500 - is defence contractor BAE Systems.