The Mutual Pact of Succession (Latin: Pactum Mutuae Successionis, German: Gegenseitiger Erbvertrag) was a succession device secretly signed by archdukes Joseph and Charles of Austria, the future emperors of the Holy Roman Empire, in 1703.
In 1700 the senior line of the House of Habsburg became extinct with the death of King Charles II of Spain.
Charles, who was at the time still unsuccessfully fighting for the crowns of Spain, succeeded him according to the Pact and returned to Vienna.
However, Charles soon expressed a wish to amend the Pact in order to give his own future daughters precedence over his nieces.
[1] The Pact was finally superseded by the Pragmatic Sanction of 1713, promulgated by Charles to ensure the succession of his own daughters instead of Joseph's.