The money market consists of short term bonds due in 30 to 60 days. These are the same type of bonds you would find in any long term bond fund. The only difference is that these bonds will be paid back in 30 days instead of 30 years. They are considered safe because the company is unlikely to incur any financial hardship in the next 30 days that would prevent them from paying back their bonds. Money Market funds are not insured by the FDIC.