The Austrian theory of business cycles is one of the Austrian school's major contributions to economic thought. Mainly elaborated by Ludwig von Mises in "The Theory of Money and Credit" (1912), then further developed by Friedrich Hayek in "Business Cycles" (1931), this theory offers a comprehensive explanation of the mechanisms leading to crises and recessions. Unlike other schools of thought, which point to supply-demand imbalances, a fall in aggregate demand or monetary policy errors during a crisis, Austrian economists specifically point to central banks as responsible for these cycles.

This theory is based on a fundamental distinction concerning the temporality of crises. For Austrian economists, the crisis begins long before the recession, sometimes months or years before. The recession represents the end of the cycle, not its beginning. What other currents call crisis is merely the painful but necessary correction of errors accumulated during expansion.

The cycle begins with an artificial cut in interest rates initiated by the central bank. In a sound monetary system, a fall in rates would indicate an abundance of savings, signalling to entrepreneurs to redirect investment towards the furthest stages of production. However, when this cut is artificial, the intertemporal signal is totally distorted by the arbitrary expansion of money in circulation.

This easily accessible liquidity encourages borrowing, which is invested in a wide range of projects, whether or not individuals actually wish to consume. As Mises writes in "Omnipotent Government", governments can reduce short-term rates and encourage credit expansion, creating artificial growth. But such a boom is bound to collapse, leading to depression. The boom sends out false signals: confidence increases, uncertainty decreases, encouraging higher investment and consumption and lower savings.

Malinvestment refers to investment decisions made on the basis of signals distorted by central monetary policies. These errors lead to a concentration of investment in projects that are either unviable or premature in relation to real demand. These malinvestments waste resources by immobilizing scarce factors of production in unproductive activities.

A contemporary corollary is the proliferation of zombie enterprises: companies surviving on low-interest credit, even though their business model would not be profitable under normal conditions. As Mises points out in "Human Action", the undulatory movements affecting the economic system are the inevitable result of repeated attempts to lower the interest rate through credit expansion. While money creation may give the illusion of an abundance of capital, material, human and technical resources remain limited. Printing money does not print scarce goods.

The bust phase is the inevitable economic collapse following a boom triggered by monetary manipulation. Take the real estate market, for example: fooled by artificially low interest rates, many entrepreneurs invest massively in construction. This boom appears prosperous in the short term, but the growth is unsustainable because there are more projects than real resources. When the central bank raises rates to cope with inflation, companies dependent on low rates run into difficulties, leading to bankruptcies and a sharp contraction in the market.

The Great Depression is a perfect illustration of this theory. As Murray Rothbard details in "America's Great Depression", between 1921 and 1929, the Federal Reserve pursued a policy of aggressive monetary expansion, increasing the money supply by 61%. This new money flooded the stock market, contributing to unsustainable overvaluation. Artificially low interest rates sent a misleading signal to entrepreneurs. When the Federal Reserve slowed expansion in 1929, the artificial production structure collapsed. The crash of October 1929 was not the cause of the crisis, but the symptom of the end of the artificial boom. For Austrian economists, this phase was necessary to liquidate malinvestments and allow the economy to return to an equilibrium based on genuine time preferences.