Concerns over Pope Francis' health have mounted in recent years as have questions about his succession. Here's what we know.

Like his predecessors, Pope Francis was selected using an age-old method -- a system known as the Papal conclave.

With Pope Francis still in critical condition, some may ask what happens when the Holy See becomes sede vacante after the resignation or death of a pope. Last Feb. 14, the 88-year-old Bishop of Rome was admitted to the Gemelli Hospital because of bronchitis that later developed into bilateral lung infection,