Also known as a letter of request. A request from a court in one country to the judiciary of a foreign country to perform a specified act that would violate the foreign country's sovereignty if done without its approval. Letters rogatory are commonly used for:

(28 C.F.R. § 92.54.)

Letters rogatory may be used regardless of whether multi-lateral or bilateral treaties on judicial assistance are in force. Letters rogatory used in countries not party to a treaty on the collection of evidence must be submitted and delivered through diplomatic channels. However, letters rogatory used in countries that are parties to a treaty, such as the Hague Evidence Convention, usually may be submitted directly to a court in that country to obtain performance of a requested action (see 28 U.S.C. §1782).