UNIVERSI DOMINICI GREGIS (Apostolic Constitution of Pope John Paul II on the Vacancy of the Apostolic See and the Election of the Roman Pontiff, 22 February, 1996)
UNIVERSI DOMINICI GREGIS embodies the "special laws" referred to in canon 335 of the Code of Canon Law: "When the Roman See is vacant or entirely impeded, nothing is to be altered in the governance of the universal church, the special laws issued for these circumstances, however, are to be observed." The "special laws" included in this apostolic constitution govern the norms the Cardinals are to follow when the Roman See becomes vacant. They also govern the procedure of electing a new pope.
Papal Transition PDF from the U.S. Conference of Catholic Bishops
Revised March 13, 2013 (HEC)