In economics, hyperinflation is a very high and typically accelerating inflation. It quickly erodes the real value of the local currency, as the prices of all goods increase. This causes people to minimize their holdings in that currency as they usually switch to more stable foreign currencies. Effective capital controls and currency substitution ("dollarization") are the orthodox solutions to ending short-term hyperinflation; however, there are significant social and economic costs to these policies. Ineffective implementations of these solutions often exacerbate the situation. Many governments choose to attempt to solve structural issues without resorting to those solutions, with the goal of bringing inflation down slowly while minimizing social costs of further economic shocks; however, this can lead to a prolonged period of high inflation.

Unlike low inflation, where the process of rising prices is protracted and not generally noticeable except by studying past market prices, hyperinflation sees a rapid and continuing increase in nominal prices, the nominal cost of goods, and in the supply of currency. Typically, however, the general price level rises even more rapidly than the money supply as people try ridding themselves of the devaluing currency as quickly as possible. As this happens, the real stock of money (i.e., the amount of circulating money divided by the price level) decreases considerably.

Hyperinflation is often associated with some stress to the government budget, such as wars or their aftermath, sociopolitical upheavals, a collapse in aggregate supply or one in export prices, or other crises that make it difficult for the government to collect tax revenue. A sharp decrease in real tax revenue coupled with a strong need to maintain government spending, together with an inability or unwillingness to borrow, can lead a country into hyperinflation.

In 1956, Columbia University economics professor Phillip Cagan wrote The Monetary Dynamics of Hyperinflation, often regarded as the first serious study of hyperinflation and its effects (though The Economics of Inflation by C. Bresciani-Turroni on the German hyperinflation was published in Italian in 1931). In this work, Cagan defined a hyperinflationary episode as starting in the month that the monthly inflation rate exceeds 50%, and as ending when the monthly inflation rate drops below 50% and stays that way for at least a year. Economists usually follow Cagan's description that hyperinflation occurs when the monthly inflation rate exceeds 50% (accumulating to a yearly increase of 12,874.63%, or an increase by a factor of 129.7463).

The International Accounting Standards Board has issued guidance on accounting rules in a hyperinflationary environment. It does not establish an absolute rule on when hyperinflation arises, but instead lists factors that indicate the existence of hyperinflation:

While there can be a number of causes of moderate inflation, almost all hyperinflations have been caused by government budget deficits financed by currency creation. Peter Bernholz analysed 29 hyperinflations (following Cagan's definition) and concludes that at least 25 of them have been caused in this way. A necessary condition for hyperinflation is the use of paper money instead of gold or silver coins. Most hyperinflations in history, with some exceptions, such as the French hyperinflation of 1789–1796, occurred after the use of fiat currency became widespread in the late 19th century. The French hyperinflation took place after the introduction of a non-convertible paper currency, the assignat.

Monetarist theories hold that hyperinflation occurs when there is a continuing (and often accelerating) rapid increase in the amount of money that is not supported by a corresponding growth in the output of goods and services.

The increases in price that can result from rapid money creation can create a vicious circle, requiring ever growing amounts of new money creation to fund government deficits. Hence both monetary inflation and price inflation proceed at a rapid pace. Such rapidly increasing prices cause widespread unwillingness of the local population to hold the local currency as it rapidly loses its buying power. Instead, they quickly spend any money they receive, which increases the velocity of money flow; this in turn causes further acceleration in prices. This means that the increase in the price level is greater than that of the money supply.