Investment Company A company or trust that uses its capital to invest in other companies. There are two principal types: the closed end and the open end, also known as a mutual fund. Shares of closed-end investment companies, most of which are listed on the NYSE, are readily transferable in the open market and are bought and sold like shares of stock. Capitalization of these companies remains the same unless action is taken to change, which is rare. Open-end funds sell their own new shares to investors, stand ready to buy back their old shares, and are not listed. Open-end funds are so called because their capitalization is not fixed; they issue more shares as people want them.