Nuveen Municipal High Income Opportunity Fund (the Fund) is a diversified closed-end management investment company. The Fund’s primary investment objective is to provide high current income exempt from regular federal income tax. Its secondary investment objective is to seek attractive total return consistent with its primary objective. The Fund is focused on investing at least 80% of its assets in municipal securities and other related investments. It may invest up to 75% of its managed assets in municipal securities rated, at the time of investment, Baa/BBB or lower by at least one nationally recognized statistical rating organization (NRSRO). It invests in various sectors, such as transportation, education and civic organizations, utilities, healthcare, housing/multifamily and other. The Fund's portfolio is spread across areas, including Illinois, California, Florida, New York, Colorado, Wisconsin, Texas, Kentucky and New Jersey. Its investment advisor is Nuveen Fund Advisors, LLC.