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 (or other non-debt assets which generate receivables) and selling their related cash flows to third party investors as securities, which may be described as bonds, pass-through securities, or collateralized debt obligations (CDOs). Investors are repaid from the principal and interest cash flows collected from the underlying debt and redistributed through the capital structure of the new financing. Securities backed by mortgage receivables are called mortgage-backed securities (MBS), while those backed by other types of receivables are asset-backed securities (ABS).

The granularity of pools of securitized assets can mitigate the credit risk of individual borrowers. Unlike general corporate debt, the credit quality of securitized debt is non-stationary due to changes in volatility that are time- and structure-dependent. If the transaction is properly structured and the pool performs as expected, the credit risk of all tranches of structured debt improves; if improperly structured, the affected tranches may experience dramatic credit deterioration and loss.[1]

Securitization has evolved from its beginnings in the late 18th century to an estimated outstanding of $10.24 trillion in the United States and $2.25 trillion in Europe as of the 2nd quarter of 2008. In 2007, ABS issuance amounted to $3.455 trillion in the US and $652 billion in Europe.[2] WBS (Whole Business Securitization) arrangements first appeared in the United Kingdom in the 1990s, and became common in various Commonwealth legal systems where senior creditors of an insolvent business effectively gain the right to control the company.[3]