A formal request made a court in one country to a foreign court for judicial assistance, is called letter rogatory. This mechanism is mainly used for the service of process, and for taking evidence. If 'A', staying in the US, wants to sue 'B', a resident of Brazil, the former has to approach the US court, which issues a summons against 'B', and requests the Brazilian court through a letter rogatory, to serve the process on 'B'. The same applies in case of examining a witness staying in another country.