Reserve Bank of India controls the credit supply in an economy. 

This policy is called Monetary Policy.

(i) Cash Reserve Ratio (CRR) : It refers to the minimum amount of funds that a commercial bank has to maintain with the Reserve Bank of India in the form of deposits. For example, suppose the total assets of a bank are worth ?200 crores and the minimum cash reserve ratio is 10%.

Then the amount that the Commercial Bank has to maintain with RBI is ?20 crores. An increase in CRR reduces the lending ability of the Commercial Banks. If this ratio rises to 20%, then the reserve with RBI increases to ?40 crores.Thus, less money will be left with the commercial bank for lending. This will eventually lead to considerable decrease in the money supply.

(ii) Statutory Liquidity Ratio (SLR) : SLR is concerned with maintaining the minimum reserve of assets with RBI, whereas the cash reserve ratio is concerned with maintaining cash balance (reserve) with RBI. So,SLR is defined as the minimum percentage of assets to be maintained in the form of either fixed or liquid assets with RBI. The flow of credit is reduced by increasing this liquidity ratio and vice-versa. A rise in SLR will restrict the banks to pump money in the economy, thereby contributing towards decrease in money supply.