Benedict XVI, the previous pope, resigned as a result of deteriorating physical health brought on by 4 heart attacks and a stroke. So he decided that someone of better health would be better suited to do his job. A wise and courageous descision.
Pope Benedict cites his retirement to be for medical reasons but there may be an underlying factor. Several weeks prior to announcing his retirement the Vatican got wind of an article that was to be printed in a large European newspaper. The article sites documentation showing that in the 1980's a Priest from Italy took a 9yr old boy on a "retreat" to the mountains. He tied the boy up and raped him for 2 weeks. When the family took this to the priests superior (Pope Benedict) he transferred the priest to Germany, requested no psych evaluation or behavioral study and had the priest begin work at an all children's summer camp. The story was of course buried in light of the first Papal resignation in 700 years. So it's every individuals guess as to exactly why.
Our Catholic Cardinals elected, Jorge Mario Cardinal Bergoglio, S.J., a 76 year old, Argentinian, to be the new Pope. He took the name, Francis, after St. Francis of Assisi. The first Argentinian; the first Jesuit (Society of Jesus); and the first, Francis! Concerning his predecessor, His Holiness, Benedict XVI, Pope Emeritus, please read my answer to 123green321's question below. Answers to the contrary are a lotta malarkey. Thank you very much! Frank