A membership interest is an investor’s ownership stake in an LLC (not an LP). Each investor in an LLC is called a “member.” A person who holds a membership interest has a profit and voting interest in the LLC. Ownership in an LLC can be expressed by percentage ownership interest or membership units. A membership interest is frequently represented in the admission of the investor’s name to the LLC to a ledger, this means no certificated security instruments may be issued to membership interest holders aka members. See Investor and LP.