Calvert US Mid-Cap Core Responsible Index Fund Class R6 is an open-end mutual fund designed to provide broad exposure to U.S. mid-capitalization equities while incorporating rigorous environmental, social, and governance (ESG) screening criteria. Its primary purpose is to track the Calvert US Mid-Cap Core Responsible Index, offering investors access to mid-cap stocks that meet defined standards for responsible investment. The fund emphasizes a diversified portfolio, with its largest holdings spread thinly across several sectors including technology, financial services, and consumer defensive industries. Notable constituents typically include companies like AppLovin Corp, Autodesk Inc, and Bank of New York Mellon, reflecting a blend of growth and value characteristics commonly found in the mid-cap category. The fund stands out for its low expense ratio and a focus on responsible investing, making it particularly relevant for institutional investors and retirement plans seeking both mid-cap equity exposure and adherence to ESG principles. By balancing performance objectives with sustainable investing practices, the fund contributes to the growing integration of ESG considerations in mainstream portfolio management.