The selection of the Pope, the Bishop of Rome and Supreme Pontiff of the Catholic Church, prior to the promulgation of In Nomine Domini in AD 1059 varied throughout history. Popes were often putatively appointed by their predecessors or by political rulers. While some kind of election often characterized the procedure, an election that included meaningful participation of the laity was rare, especially as the Popes' claims to temporal power solidified into the Papal States. The practice of papal appointment during this period would later result in the putative jus exclusivae, i.e., the claimed but invalid right to veto the selection that Catholic monarchs exercised into the twentieth century.

In nomine Domini is a papal bull written by Pope Nicholas II. The bull was issued on 13 April 1059 and caused major reforms in the system of papal election, most notably establishing the cardinal-bishops as the sole electors of the pope, with the consent of minor clergy.