Monetary Policy
Monetary policy refers to a central bank's actions on interest rates and the money supply to ensure price stability. Its decisions pass through to financial markets immediately, but only reach the real economy — credit, investment, consumption — after a lag of 12 to 18 months.
Last updated: 9 July 2026
Definition
DefinitionMonetary policy is conducted by the central bank of a country or monetary zone (the Federal Reserve in the United States, the European Central Bank for the eurozone, the Bank of England in the United Kingdom). Its main instrument is the policy rate — the interest rate at which the central bank lends to commercial banks on a very short-term basis. By modifying this rate, the central bank influences the entire structure of interest rates in the economy, and hence the cost of credit.
There are two fundamental stances: accommodative (expansionary) monetary policy, which consists of lowering rates to stimulate credit and demand, and restrictive (contractionary) monetary policy, which aims to raise rates to curb inflation by reducing demand. The central bank can also act on the money supply through open market operations (buying or selling securities on financial markets) and reserve requirements imposed on commercial banks.
Why it matters
Monetary policy acts with a time lag of 12 to 18 months on the real economy, which makes its conduct particularly delicate. The central bank must anticipate the future state of the economy and act preemptively, exposing it to calibration errors. The independence of the central bank from the government is a recurring theme in Mankiw: a government might be tempted to finance its spending through money creation, which would lead to inflation. Institutional independence protects against this temptation.
The transmission mechanism of monetary policy operates through several channels: the interest rate channel (the cost of credit affects investment and consumption), the exchange rate channel (a rate hike strengthens the currency and penalizes exports), the credit channel (bank lending conditions tighten or loosen), and the expectations channel (central bank communication influences behavior even before rates change).
Key points
The ECB's mandate is centered on price stability (2% inflation target). The Fed's mandate is dual: price stability AND full employment. This difference in mandates explains sometimes divergent approaches
The Taylor rule (i = π + r* + 0.5(π − π*) + 0.5(y − y*)) provides an analytical framework for assessing whether monetary policy is too accommodative or too restrictive at any given time. Mankiw introduces it as an essential pedagogical tool
QE, used massively after the 2008 crisis and during the Covid-19 pandemic, significantly inflated central bank balance sheets. The ECB's balance sheet reached nearly €8,800 billion at its mid-2022 peak, primarily through the APP and PEPP programs
Central bank credibility is decisive: if agents trust its commitment against inflation, expectations remain anchored and monetary policy is more effective
Concrete example
ExamplesBetween July 2022 and September 2023, the ECB raised its main refinancing rate from 0% to 4.5% and its deposit rate — the effective market reference — from −0.5% to 4%, to combat post-Covid and post-Ukraine invasion inflation. This 450-basis-point increase in 14 months was the fastest in the institution's history. It caused a significant increase in mortgage rates (from ~1% to ~4% in France), a slowdown in the real estate market, and a tightening of corporate financing conditions. In parallel, the U.S. Fed raised its target range from 0–0.25% to 5.25–5.50%, its highest level since 2001.
Mankiw anecdote
MankiwMankiw presents the Taylor rule as a benchmark for judging whether monetary policy is too accommodative or too restrictive. It is John Taylor himself who drew the best-known analysis from it: in "Getting Off Track" (2009), building on his Jackson Hole contribution (2007), he argues that Greenspan's Fed kept rates in 2003-2005 well below what his rule would have prescribed, which may have fueled the housing bubble behind the 2008 crisis. The episode illustrates the limitations of discretionary judgment versus systematic monetary policy rules.
Further reading
ProgressionMoney creation through credit, the money multiplier, and the role of bank reserves are detailed in the explanation "Money and the Banking System" (ch. 10, Intermediate level). The role of credibility and the anchoring of expectations in the effectiveness of monetary policy is explored in depth in the explanation "Rational Expectations and the New Classical Macroeconomics" (ch. 14, Advanced level).
Market impact
MarketsCentral bank rate decisions and the accompanying communication (press conferences, economic projections) are the most impactful events for financial markets. A rate hike mechanically lowers the value of existing bonds and penalizes growth stocks whose future earnings are discounted at a higher rate. A rate cut has the opposite effect. The foreign exchange market also reacts: a more restrictive stance than anticipated strengthens the currency, while a more accommodative one weakens it.