A central bank manages a nation's currency and monetary policy. It controls the money supply, sets interest rates, and acts as a lender of last resort to commercial banks. It does not serve individuals. It serves the banking system and the economy as a whole. The Federal Reserve, the European Central Bank, the Bank of England, and the Bank of Japan are the most powerful central banks in the world.

The central bank has several tools. It sets the policy interest rate, which influences borrowing costs across the economy. It buys and sells government securities to inject or drain liquidity. It sets reserve requirements for banks. In emergencies, it lends to banks that cannot find funding elsewhere. During the 2008 crisis and the 2020 pandemic, central banks used these tools on an unprecedented scale, buying trillions in bonds to keep credit flowing.

Central banks also supervise banks and monitor financial stability. They watch for bubbles, excessive leverage, and systemic risk. They publish research and communicate with the public through speeches and statements. Their words move markets. A single sentence from the Fed chair can send stocks up or down.

Independence is a core principle. Central banks should make decisions based on economic data, not political pressure. That independence is not absolute. Congress can change the Fed's mandate. But in most countries, central banks operate with a high degree of autonomy, because politicians have a history of meddling with monetary policy for short-term gain.