's a timeline of the scandal, according to officials involved in the investigation:
Spring 2006 — Paula Broadwell meets Petraeus at Harvard University, where she is a graduate student. Petraeus is a lieutenant general working on a counterinsurgency manual and is invited to speak about his experiences in Iraq.
January 2007 — The Senate confirms Petraeus as the commanding general for U.S. troops in Iraq.
2008 — Broadwell starts studying Petraeus' leadership. On a visit to Washington, Petraeus invites Broadwell to join him and his team for a run along the Potomac River.
October 2008 — Petraeus is named commander of U.S. Central Command, based at MacDill Air Force Base near Tampa, Fla., where socialite Jill Kelley and her husband attend events alongside the area's military elite.
June 30, 2010 — The Senate confirms Petraeus as the new commander for war in Afghanistan. Over the next year, Broadwell expands her research of Petraeus into an authorized biography. She makes multiple trips to Afghanistan and is given unprecedented access to Petraeus and his commanders.
Sept. 6, 2011 — Petraeus is sworn in as CIA director with his wife, Holly, by his side. Broadwell keeps in contact with Petraeus and is later invited to his office for events, including a meeting with actress Angelina Jolie.
Fall 2011 — Tampa socialite Jill Kelley attends an FBI "Citizens' Academy" in Florida, where Frederick W. Humphries, a veteran FBI counterterrorism investigator, gives a lecture.
November 2011 — Petraeus begins an extramarital affair with Broadwell, according to retired Army Col. Steve Boylan.
January 2012 — Broadwell's biography, "All In: The Education of General David Petraeus," is released. In an interview with her hometown paper, the Bismarck Tribune, Broadwell describes Petraeus as an inspirational figure who always takes care of his subordinates.
May 2012 — Anonymous emails, ultimately traced to Broadwell, were sent to Gen. John Allen, the top U.S. commander in Afghanistan, and several other generals warning them to stay away from Kelley, the Florida socialite. The emails came from the pseudonym "Kelleypatrol" and included notes on Allen's plans to see Kelley in Washington the following week. Concerned about how anyone else would know about his personal plans, Allen forwarded the emails to Kelley to see whether she was playing a prank on them. Other generals also forward to Kelley copies of emails they received.
Early June 2012 — Kelley begins receiving additional emails directly from various anonymous email accounts claiming she's up to no good. One email mentions Petraeus and an upcoming social event in Washington.
June 2012 — Kelley discusses the emails with Humphries, the FBI agent, leading to an investigation. FBI agents are concerned that the sender of the emails is tracking the movements of Allen and Petraeus.
July 2012 — The affair between Petraeus and Broadwell ends, according to Petraeus' friend Boylan. Because of the sensitive nature of the investigation involving security issues, FBI officials and Justice Department officials are notified, including FBI director Robert Mueller. Attorney General Eric Holder is notified around this time.
August 2012 — Humphries tells Kelley he's been removed from the case and complains that the FBI is moving too slowly. Meanwhile, another FBI agent involved in the investigations tells Kelley the FBI has traced the emails to Broadwell, whom Kelley has never met.
Late summer 2012 — Emails between Petraeus and Broadwell lead agents to believe the two are having an affair.
Late September — The FBI conducts the first of its two interviews with Broadwell. By this time, the FBI has long since concluded that none of Petraeus' computers had been hacked and that Petraeus was not involved in the cyber harassment of Kelley. After Broadwell was interviewed, agents search her computers and found substantial amounts of classified documents — a discovery that shifted the focus of the investigation.
October 2012 — FBI agents spend most of the month trying to resolve issues related to the classified documents that Broadwell has — working with the Pentagon to assess where she got the documents, their significance and whether she was authorized to possess them.
Oct. 26 — The FBI conducts its first and only interview of Petraeus. At the interview, Petraeus acknowledges the affair. Petraeus is questioned about the classified documents that are in Broadwell's possession, and he denies giving her any classified documents.
Oct. 27 — Humphries communicates with House Majority Leader Eric Cantor and says he's worried the FBI isn't aggressively pursuing a possible security breach. Word of Humphries concerns first reaches Rep. Dave Reichert, R-Wash., who arranges for Humphries to speak with Cantor.
Oct. 31 — Cantor's chief of staff calls the FBI chief of staff to inform him of the tip. Cantor is assured soon after that the FBI is on top of any possible vulnerability.
Friday, Nov. 2 — The FBI conducts what Attorney General Eric Holder later calls "a very critical interview" with Broadwell that convinces the Justice Department it knows enough about the case to inform the White House. In this second interview with Broadwell, the FBI is told how many classified documents she received and that none of them came from Petraeus.
Tuesday, Nov. 6 — As Americans cast their ballots on Election Day, the FBI informs Director of National Intelligence James Clapper of the investigation. Clapper calls Petraeus and urges him to resign.
Wednesday, Nov. 7 — The White House is first notified about the affair involving Petraeus. The retired general turns 60.
Thursday, Nov. 8 — President Barack Obama, having returned from Chicago, is told of the affair. Petraeus meets with Obama at the White House and asks to resign.
Friday, Nov. 9 — Obama accepts Petraeus' resignation. News of the resignation breaks before Congress is briefed. Broadwell's husband emails guests to cancel her 40th birthday party, scheduled for that weekend. By the evening, Broadwell has been publicly identified.
Sunday, Nov. 11 — Lawmakers complain in televised interviews that the FBI didn't alert them sooner to the investigation. Kelley's identity is revealed by The Associated Press, and she issues a statement asking for privacy.
Monday, Nov. 12 — The FBI searches Broadwell's house in Charlotte, N.C., with her consent. As she has told them to expect, the agents find classified documents there. The Pentagon orders an investigation into the Allen matter.
Tuesday, Nov. 13 — Pentagon reveals that Allen is under internal investigation for thousands of "inappropriate communications" with Kelley over a two-year period, and puts on hold his nomination to be the next commander of U.S. European Command and the commander of NATO forces in Europe. Macdill Air Force Base revokes Kelley's access pass.
Wednesday, Nov. 14 — President Barack Obama says he has seen no evidence that national security was threatened by the scandal. FBI Director Robert Mueller and Acting CIA Director Michael Morell meet privately with top lawmakers on intelligence committees. Defense Secretary Leon Panetta, traveling abroad, says he's confident Allen can continue to lead. Broadwell's security clearance is suspended.
Thursday, Nov. 15 — Citing a string of ethical lapses by senior military officers, Panetta orders a review of ethics training. The CIA opens an "exploratory" investigation into Petraeus' general conduct. Petraeus says in a CNN interview that he never gave classified information to Broadwell. Questioning continues on Capitol Hill, with Petraeus set to testify Friday about Libya before the House Intelligence Committee.
Associated Press writers Adam Goldman, Pete Yost, Michael J. Sniffen, Kimberly Dozier, Eileen Sullivan, Donna Cassata and Robert Burns contributed to this report.