This article provides a review of the securitization instruments in the context of the subprime mortgage crisis of 2008. The decreasing housing prices in the U.S. caused the increasing mortgage defaults and the increasing mortgage defaults caused this subprime mortgage crisis and this crisis is exploded by securitization instruments (e.g., CDS) which are just too complex to see their risks. This article will provide a specific classification of securitization instruments and distinguishes between two main classes of securitization instruments. The first classes are mortgage-backed security (MBS), asset-backed security (ABS), asset-backed commercial paper (ABCP) and cash-flow collateralized debt obligation (CDO).The second category of securitization instruments includes credit default swap (CDS) and synthetic collateralized debt obligation (synthetic CDO). Finally, this article ends with a short discussion of the roles of the credit rating agency (CRA) in the financial crisis.