ZMUN is passively managed, providing exposure to US tax-exempt, investment-grade municipal bonds that are either currently callable or will be callable within three months, with coupons of 3.5% or higher. Eligible securities must be fixed-rate, USD-denominated, with maturities between one and ten years. The fund may hold cash, cash equivalents, and money market instruments for liquidity. Conversely, the fund excludes taxable bonds, floating-rate bonds, derivatives, private placements, pre-refunded bonds, and AMT-subject bonds. The underlying index is market-value weighted. The fund may engage in securities lending secured by collateral and reinvest cash collateral in short-term instruments. The fund may also enter reverse repurchase agreements up to one-third of its assets.