In economics, deflation is a decrease in the general price level of goods and services. Deflation occurs when the inflation rate falls below 0% (a negative inflation rate). Inflation reduces the value of currency over time, but sudden deflation increases it. This allows more goods and services to be bought than before with the same amount of currency. Deflation is distinct from disinflation, a slow-down in the inflation rate, i.e. when inflation declines to a lower rate but is still positive.

Economists generally believe that a sudden deflationary shock is a problem in a modern economy because it increases the real value of debt, especially if the deflation is unexpected. Deflation may also aggravate recessions and lead to a deflationary spiral.

Some economists argue that prolonged deflationary periods are related to the underlying of technological progress in an economy, because as productivity increases (TFP), the cost of goods decreases.

Deflation usually happens when supply is high (when excess production occurs), when demand is low (when consumption decreases), or when the money supply decreases (sometimes in response to a contraction created from careless investment or a credit crunch) or because of a net capital outflow from the economy. It can also occur due to too much competition and too little market concentration.