Insiders say the pope is saying in public what has long been discussed in private inside the Vatican, where a paper has been considered for years allowing condom use between married couples, when one has AIDS.
The debate continues to sharply divide the Vatican but it could now play out in the open.
The book, to be debuted Tuesday by the Vatican, also tackles the pope's decision to lift the excommunication of a bishop accused of being a Holocaust denier.
Benedict tells Seewald that he would never have lifted the excommunication of a bishop who denied the Holocaust if he had known "what sort of person we were dealing with."
Bishop Richard Williamson said in a German TV interview in January 2009 that he didn't believe Jews were gassed during World War II. The interview aired the same day Pope Benedict lifted his excommunication. The uproar from the incident strained the pope's relationship with the Jewish community.
Today, Williamson found himself in even more hot water after the attorney he hired to defend him was linked to the neo-Nazi movement.
Jewish leaders not only criticized Benedict's decision regarding Williamson but also his stance on World War II-era Pope Pius XII.
In the book, the pope calls Pius XII a "great righteous" man who saved more Jews than anyone else. Pius XII has been criticized by some in the Jewish community for not doing enough to speak out against the mass deportation and killing of 6 million Jews during the Holocaust.
"The decisive thing is what he did and what he tried to do, and on that score, we really must acknowledge, I believe, that he was one of the great righteous men and that he saved more Jews than anyone else," Benedict said in the book.
Last year, the Catholic Church made Pius XII a strong contender for sainthood after the Pope praised his "heroic virtues."
The Associated Press contributed to this report.