A voucher is a bond which is worth a certain monetary value and which may be spent only for specific reasons or on specific goods. Examples include (but are not limited to) housing, travel, and food vouchers. The term voucher is also a synonym for receipt and is often used to refer to receipts used as evidence of, for example, the declaration that a service has been performed or that an expenditure has been made.

The term is also commonly used for education vouchers, which are somewhat different.

Vouchers are used in the tourism sector primarily as proof of a named customer's right to take a service at a specific time and place. Service providers collect them to return to the tour operator or travel agent that has sent that customer, to prove they have given the service. So, the life of a voucher is as below:

This approach is most suitable for free individual tourist activities where pre-allocation for services are not necessary, feasible or applicable. It was customary before the information era when communication was limited and expensive, but now has been given quite a different role by B2C applications. When a reservation is made through the internet, customers are often provided a voucher through email or a web site that can be printed. Providers customarily require this voucher be presented prior to providing the service.

Milton Friedman (July 31, 1912 – November 16, 2006) was an American economist, statistician, and author who taught at the University of Chicago for more than three decades. He was a recipient of the Nobel Memorial Prize in Economic Sciences, and is known for his research on consumption analysis, monetary history and theory, and the complexity of stabilization policy. As a leader of the Chicago school of economics, he influenced the research agenda of the economics profession. A survey of economists ranked Friedman as the second most popular economist of the twentieth century behind John Maynard Keynes, and The Economist described him as "the most influential economist of the second half of the 20th century…possibly of all of it."

Friedman's challenges to what he later called "naive Keynesian" (as opposed to New Keynesian) theory began with his 1950s reinterpretation of the consumption function, and he became the main advocate opposing activist Keynesian government policies. In the late 1960s he described his own approach (along with all of mainstream economics) as using "Keynesian language and apparatus" yet rejecting its "initial" conclusions. During the 1960s he promoted an alternative macroeconomic policy known as "monetarism". He theorized there existed a "natural" rate of unemployment, and argued that governments could increase employment above this rate (e.g., by increasing aggregate demand) only at the risk of causing inflation to accelerate. He argued that the Phillips curve was not stable and predicted what would come to be known as stagflation. Friedman argued that, given the existence of the Federal Reserve, a constant small expansion of the money supply was the only wise policy.