For centuries, the leader of the Catholic Church has been chosen in a highly secretive gathering known as the “conclave,” meaning “with key” in Latin – a nod to how cardinals used to be locked in until a new pope was selected. Cardinals tasked with picking the next pontiff follow an elaborate process with roots in the Middle Ages.

The rituals as we know them today have been subsequently revised by successive popes. The bulk of the modern rulebook that cardinals follow was overhauled by John Paul II in the 1996 Apostolic constitution known as “Universi Dominici Gregis,” with a few further adjustments by Benedict XVI.

Once the date is set, the cardinal electors head to the home of the conclave – the Vatican’s Sistine Chapel. A candidate needs two-thirds of the votes cast to be elected.

Many different factors are at play during this week’s conclave, which is poised to be a battle between those who want to continue with Francis’ reforms and vision, and those who want to slow things down and make a course correction.

From solemn oaths to intricate voting procedures and the famed white smoke, here’s how the centuries-old process unfolds.

Shortly after, the new pope steps onto the balcony, framed by red curtains, and delivers his first apostolic blessing, known as the “Urbi et Orbi” (“To the City and to the World”).

This brings the intricate process of the conclave to an end. The days ahead will see the new pontiff attend his inauguration Mass, which usually takes place at St. Peter’s Basilica, before assuming his duties as the head of the Catholic Church.