The 85-year-old Pope announced his decision in Latin during a meeting of Vatican cardinals on Monday morning.
"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited to an adequate exercise of the Petrine ministry," he told the cardinals.
Only 3 other popes in the history of the Church have ever resigned:
The last was in 1415.
And to add a little flavor:
Anyway, very interesting.