Trust Indenture Act of 1939

This Act applies to debt securities such as bonds, debentures, and notes that are offered for public sale. Even though such securities may be registered under the Securities Act, they may not be offered for sale to the public unless a formal agreement between the issuer of bonds and the bondholder, known as the trust indenture, conforms to the standards of this Act.

Source: United States Securities and Exchange Commission.