ZTRE targets US corporate bonds maturing in three years. The fund tracks an index consisting of USD-denominated, investment grade corporate debt securities that have at least 2.5 years but less than 3.5 years remaining to maturity and at least $300 million face value amount outstanding. Eligible securities must be rated in the four highest credit categories by at least one nationally recognized rating agency. The index selects one security per issuer, considering rank, amount outstanding, and time since issue. With regards to rank, senior bonds are selected first, followed by senior secured debt, and finally, all subordinated debt. The fund may invest in debt securities issued by US and non-US corporations of any sector. Holdings are weighted equally. The index reconstitutes and rebalances on the last calendar day of each month.