Vanguard Mortgage-Backed Securities Index Fund (VMBS)

The fund employs an indexing investment approach designed to track the performance of the Bloomberg U.S. MBS Float Adjusted Index. This index covers U.S. agency mortgage-backed pass-through securities issued by the GNMA, the FNMA, and the FHLMC. To be included in the index, pool aggregates must have at least $1 billion currently outstanding and a weighted average maturity of at least 1 year. All of the fund's investments will be selected through the sampling process, and at least 80% of the fund's assets will be invested in bonds included in the index.