Open-end mutual funds are not traded on secondary markets. Instead, new shares are continuously created and sold to the public by the fund itself. The entity responsible for marketing and distributing these new shares to investors is the fund's principal underwriter, also known as the distributor. Investors purchase shares from the underwriter (or a selling group member acting on its behalf) at the public offering price (POP). When an investor wishes to sell their shares, they redeem them back to the fund at the net asset value (NAV).

A. The NYSE: Open-end mutual funds are not listed or traded on exchanges; this is a characteristic of closed-end funds and exchange-traded funds (ETFs).

B. The fund's custodian: The custodian is a bank or trust company responsible for holding and safeguarding the fund's cash and securities, not for selling shares.

D. An existing shareholder: Shares of an open-end fund cannot be sold from one investor to another; they must be redeemed directly with the fund.

1. U.S. Securities and Exchange Commission (SEC). Invest wisely: An Introduction to Mutual Funds. SEC Publication. This guide explains the purchasing process: "But many funds sell their shares to the public through brokers, banks, financial planners, or insurance agents." The underwriter is the entity that organizes and manages this distribution channel on behalf of the fund.

2. Investment Company Act of 1940. Section 2(a)(29). This section legally defines a "principal underwriter" as the entity that purchases securities from the investment company for distribution or acts as an agent in the distribution of the securities. This establishes the underwriter's role as the primary seller of the fund's shares.

3. FINRA. Securities Industry Essentials (SIE) Examination Content Outline. Section 3.2.1, "Types of investment companies." This section covers the characteristics of open-end funds, including that they are redeemable securities purchased from and sold back to the issuer (via its distributor/underwriter).