A letter rogatory is a formal request from a court in one country to "the appropriate judicial authorities" in another country requesting compulsion of testimony or documentary or other evidence or effect service of process. It is also referred to as "letter of request" (which is used specifically in the Hague Evidence Convention).
In some countries which do not permit the taking of depositions of willing witnesses, letters rogatory are the only method of obtaining evidence or serve process. Letters rogatory can be used in civil and criminal matters, and have been used in administrative matters. The execution of a request for judicial assistance by the foreign court is based on comity between nations, absent a specific treaty obligation such as the Hague Evidence Convention or Mutual Legal Assistance in Criminal Matters (MLAT) treaties.
