Collateralized debt obligations (CDOs) are financial products backed by a portfolio of fixed income assets. Between 2000-2009, $4 trillion worth of CDOs were issued by banks moving loans and debts off their balance sheets. This was enabled by the origination of subprime loans to borrowers with poor credit, which were then packaged into CDOs and sold to investors. However, as the housing market declined and borrowers defaulted, CDOs plummeted in value. Major financial firms like Bear Stearns and Merrill Lynch suffered huge losses, and the fallout of the subprime crisis led to the 2008 global financial crisis.