With the sad passing of Pope John Paul II, the Teaching Company offers free audio lectures on how a new Pope is chosen.
These lectures are presented by Professor Thomas F. X. Noble, the Robert M. Conway Director of the Medieval Institute and Professor of History at the University of Notre Dame. These lectures were first commissioned by The Teaching Company last year and reflect Dr. Noble's research interest in the history of Rome and the papacy.
The Teaching Company gives excellent lectures in general. All their courses go on sale at least once a year, so if one looks overpriced, you just have to be patient and wait until it goes on sale.
While a cardinal is always chosen as the successor, the cardinal conclave can pick almost anyone. While the new pope will almost surely be a cardinal between 50-80 years of age (The youngest Cardinal is over 50 and only Cardinals under 80 may vote) they can pick any priest they wish. It is even possible that there could be a Teen Pope (which sounds like the name of a really bad movie).
For those curious, they can look at the list of cardinals and those eligible to vote here
Out of the 117 voting cardinals, 114 of them have been picked by John Paul II.
John Paul II has been speculated to be dying for the last decade, so it's still a bit surprising that he finally died, even though it was expected. He's outlived more than half his potential successors. He had a very full life, so we will be seeing that replayed a lot in the next few days.