In 1956, Columbia University economics professor Phillip Cagan wrote The Monetary Dynamics of Hyperinflation, the book 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 his book, 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% (this is equivalent to a yearly rate of 12,974.63%, so that the amount becomes 129.7463 times as high).

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:
• The general population prefers to keep its wealth in non-monetary assets or in a relatively stable foreign currency. Amounts of local currency held are immediately invested to maintain purchasing power;
• The general population regards monetary amounts not in terms of the local currency but in terms of a relatively stable foreign currency. Prices may be quoted in that currency;
• Sales and purchases on credit take place at prices that compensate for the expected loss of purchasing power during the credit period, even if the period is short;
• Interest rates, wages, and prices are linked to a price index; and
• The cumulative inflation rate over three years approaches, or exceeds, 100%.

While there can be a number of causes of high 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.

This results in an imbalance between the supply and demand for the money (including currency and bank deposits), causing rapid inflation. Very high inflation rates can result in a loss of confidence in the currency, similar to a bank run. The excessive money supply growth can result from speculating by private borrowers, or may result from the government being either unable or unwilling to fully finance the government budget through taxation or borrowing. The government may instead finance a government deficit through the creation of money.

Governments have sometimes resorted to excessively loose monetary policy, as it allows a government to devalue its debts and reduce (or avoid) tax increases. Monetary inflation is effectively a flat tax on creditors that also redistributes proportionally to private debtors. Distributional effects of monetary inflation are complex and vary based on the situation, with some models finding regressive effects but other empirical studies progressive effects. As a form of tax, it is less overt than levied taxes and is therefore harder to understand by ordinary citizens. Inflation can obscure quantitative assessments of the true cost of living, as published price indices only look at dat…

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In 1922, inflation in Austria reached 1,426%, and from 1914 to January 1923, the consumer price index rose by a factor of 11,836, with the highest banknote in denominations of 500,000 Kronen. After World War I, essentially all State enterprises ran at a loss, and the number of state employees in the capital, Vienna, was greater than in the earlier monarchy, even though the new republic was nearly one-eighth of the size.

Observing the Austrian response to developing hyperinflation, which included the hoarding of food and the speculation in foreign currencies, Owen S. Phillpotts, the Commercial Secretary at the British Legation in Vienna wrote: "The Austrians are like men on a ship who cannot manage it, and are continually signalling for help. While waiting, however, most of them begin to cut rafts, each for himself, out of the sides and decks. The ship has not yet sunk despite the leaks so caused, and those who have acquired stores of wood in this way may use them to cook their food, while the more seamanlike look on cold and hungry. The population lack courage and energy as well as patriotism."
• Start and end date: October 1921 – September 1923
• Peak month and rate of inflation: August 1922, 129%
Increasing hyperinflation in Bolivia has plagued, and at times crippled, its economy and currency since the 1970s. At one time in 1985, the country experienced an annual inflation rate of more than 20,000%. Fiscal and monetary reform reduced the inflation rate to single digits by the 1990s, and in 2004 Bolivia experienced a manageable 4.9% rate of inflation.

In 1987, the peso boliviano was replaced by the new boliviano at a rate of one million to one (when 1 US dollar was worth 1.8–1.9 million pesos bolivianos). At that time, 1 new boliviano was roughly equivalent to 52 U.S. cents.
Brazilian hyperinflation lasted from 1985 (the year when the military dictatorship ended) to 1994, with prices rising by 184,901,570,954.39% (or 1.849×10 percent; equivalent to a tenfold increase on average a year) in that time due to the uncontrolled printing of money. There were many economic plans that tried to contain hyperinflation including zeroes cuts, price freezes and even confiscation of bank accounts.

The highest value was in March 1990, when the government inflation index reached 82.39%. Hyperinflation ended in July 1994 with the Real Plan during the government of Itamar Franco. During the period of inflation Brazil adopted a total of six different currencies, as the government constantly changed due to rapid devaluation and increase in the number of zeros.
• Start and end date: January 1985 – mid-July 1994
• Peak month and rate of inflation: March 1990, 82.39%

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