Unit Investment Trust Company (UIT) A unit investment trust (UIT) is one of three basic types of traditional investment companies, along with mutual funds and closed-end funds. UIT's hold portfolios of securities, which are not actively managed or traded. These portfolios are designed to remain fixed over the life of the investment. Investors then purchase units of a trust, which is a proportional interest in the entire portfolio. UIT's normally have a defined expiration date at which time all assets will be liquidated and distributed to the existing shareholders, based on the number of units they own at the time. One of the benefits of a UIT is that because the portfolio is fixed, investors know exactly what is contained in the portfolio as well as the income the trust is likely to generate. Additionally, because the portfolio is not actively managed, the management fee charged is usually very low.