Securitization was particularly popular among money market and pension funds because it allowed such institutions to hold assets that they were previously prevented from holding by regulatory requirements. Many institutional investors, such as pension funds, are restricted by mandates to only invest in highly rated, investment-grade securities (e.g., AAA). Through the process of securitization, pooling, and tranching, lower-quality assets (such as subprime mortgages) could be repackaged into tranches, some of which received AAA ratings from credit rating agencies. This allowed money market and pension funds to invest in these higher-yielding assets while still complying with their regulatory and internal investment mandate constraints.