Companies that need capital (fancy way of saying access to large sums of money), can issue bonds. Central banks, like RBI or Federal Reserve or Bank of England, can and do issue bonds. Govt. of a country (GOI, for example) as well as state governments, can also issue bonds. Bonds are market-linked securities, just like stocks. Not unlike stocks, bonds also trade daily in exchanges (often called "secondary markets") such as NSE / BSE etc.