Once the new pope is elected, he will have two big initial decisions to make: whether to accept the job, and what his new papal name will be.

Gregory? Leo? Benedict? No one knows what the next pope will pick. But choosing a new moniker is a decision that’s tied up in history, tradition and more than a little symbolic value.

In papal tradition, newly elected pontiffs choose a name to identify themselves during their reigns. The tradition has been around for centuries, even though no law or rule requires that a pope pick a new name.

Chester Gillis, a professor of theology at Georgetown University, said that the pope’s choice of name offers an early indicator of what his papacy might be like....