Asset backed securities derive their cash flows from pools of underlying financial assets like credit card receivables, auto loans, and mortgages. These assets are packaged and sold as bonds or notes to investors. ABS allow for the risks of the individual assets to be diversified among many investors. There are several types of ABS that differ based on the type of underlying asset, such as mortgage-backed securities for mortgages or certificates for automobile receivables for auto loans. The structure of ABS can be fully amortizing, controlled amortization, or use a bullet repayment structure to repay principal.