The Fidelity U.S. Sustainability Index Fund typically allocates a minimum of 80% of its total assets to investments that are constituents of the MSCI USA ESG Leaders Index. This particular index tracks the performance of stocks from large and mid-sized American corporations, which are chosen for demonstrating superior performance in environmental, social, and governance (ESG) criteria when compared to other companies within their respective industries, as determined by MSCI ESG Research.