Reserve deposit is a central bank regulation employed by most, but not all, of the world's central banks, that sets the minimum fraction of customer deposits and notes that each commercial bank must hold as reserves (rather than lend out). These required reserves are normally in the form of deposits made with a central bank, or cash stored physically in the bank vault (vault cash).

The required reserve ratio is sometimes used as a tool in monetary policy, influencing the country's borrowing and interest rates by changing the amount of funds available for banks to make loans with. Western central banks rarely alter the reserve requirements because it would cause immediate liquidity problems for banks with low excess reserves; they generally prefer to use open market operations (buying and selling government-issued bonds) to implement their monetary policy. The People's Bank of China uses changes in reserve requirements as an inflation-fighting tool, and raised the reserve requirement ten times in 2007 and eleven times since the beginning of 2010.