The process, according to Ryan aides, began about a month ago, after the conventions, and has included two full-length mock debates. His sparring partner has been former Solicitor General Theodore Olson, a well-known Washington lawyer who has argued before the Supreme Court on multiple occasions.
Biden's "debate camp" also included two dress rehearsals, with Maryland Rep. Chris Van Hollen standing in for Ryan and the vice president's communications director, a former Washington Post reporter, Shailagh Murray, playing the role of ABC News' Martha Raddatz, who will moderate the debate.
Ryan has less on tape for the Democrats to study, but campaign sources say he has been reading up on his young challenger, who co-authored a book, "Young Guns: A New Generation of Conservative Leaders," in 2010.
This will be Biden's first time taking questions on national television in five months. He has not, by choice or chance, appeared since a May visit to "Meet the Press," when he described himself as being "absolutely comfortable" with gay marriage.
President Obama, who had not yet publicly come out in favor, followed Biden's lead a few days later.