Securitization is the financial practice of pooling various types of contractual debt such as residential mortgages, commercial mortgages, auto loans or credit card debt obligations and selling said consolidated debt as bonds, pass-through securities, or Collateralized mortgage obligation (CMOs), to various investors. The principal and interest on the debt, underlying the security, is paid back to the various investors regularly. Securities backed by mortgage receivables are called mortgage-backed securities (MBS), while those backed by other types of receivables are asset-backed securities (ABS).

Critics have suggested that the complexity inherent in securitization can limit investors' ability to monitor risk, and that competitive securitization markets with multiple securitizers may be particularly prone to sharp declines in underwriting standards. Private, competitive mortgage securitization is believed to have played an important role in the U.S. subprime mortgage crisis.

In addition, off-balance sheet treatment for securitizations coupled with guarantees from the issuer can hide the extent of leverage of the securitizing firm, thereby facilitating risky capital structures and leading to an under-pricing of credit risk. Off-balance sheet securitizations are believed to have played a large role in the high leverage level of U.S. financial institutions before the financial crisis, and the need for bailouts.