SMB tracks an index that aims to provide market-like exposure to US short-duration, tax-exempt muni bonds with maturities of no more than six years. These bonds must have a fixed coupon schedule and have an investment grade rating to be included. Index components are proportionally weighted by market value and rebalance monthly. The fund uses a sampling method in tracking the index, which means it will invest in a sample of securities that collectively have an investment profile similar to that of the underlying index. Prior to March 1, 2022, the fund tracked the Bloomberg AMT-Free Short Continuous Municipal Index. Then until November 30, 2022, the fund used a transition index to gradually broaden its exposure before tracking its current index.