Vanguard Mortgage Backed Securities ETF (the Fund) seeks to track the performance of a market-weighted, mortgage-backed securities index. The Fund employs a passive management or indexing investment approach designed to track the performance of the Barclays Capital U.S. MBS Float Adjusted Index (the Index). The Index covers the United States agency mortgage-backed, pass-through securities issued by Government National Mortgage Association (GNMA), Federal National Mortgage Association (FNMA) and Federal Home Loan Mortgage Corporation (FHLMC). To be included in the Index, pool aggregates must have at least $250 million outstanding and a weighted average maturity of at least one year. The Fund invests by sampling the Index, meaning that it holds a range of securities that, in the aggregate, approximates the full Index in terms of key risk factors and other characteristics. The Fund�s investment advisor is Vanguard Fixed Income Group.