It is perhaps one of President George W. Bush's more frustrating failures, and one of the most difficult tasks he'll hand over to his successor.
More than seven years after the attacks of Sept. 11, 2001, Osama bin Laden, the man Bush once said he wanted captured "dead or alive," has not been found.
President-elect Barack Obama has said that he plans to renew the U.S. commitment to tracking down the al Qaeda leader.
"I think it is a top priority for us to stamp out al Qaeda once and for all, Obama told CBS's "60 Minutes" Sunday. "And I think capturing or killing bin Laden is a critical aspect of stamping out al Qaeda. He is not just a symbol, he's also the operational leader of an organization that is planning attacks against U.S. targets."
As soon as Obama takes office in January, he has said he will begin work on a plan to draw down U.S. troops in Iraq and beef up U.S. troop numbers in Afghanistan.
"Particularly in light of the problems that we're having in Afghanistan, which has continued to worsen. We've got to shore up those efforts," Obama told "60 Minutes."
During the presidential campaign, Obama promised he would refocus the military's fight to taking on the resurgent Taliban in Afghanistan.
His promise to send two additional combat brigades, or roughly 7,000 troops, to Afghanistan seems small now when compared to the request by top U.S. military commanders there for as many as 20,000 U.S. forces.
But finding bin Laden won't be easy, and several former CIA operatives warn that sending more troops could have severe consequences, won't put a dent in finding the al Qaeda leader and could lead the nation to another war without end.
"He's completely disappeared," former CIA operative Robert Baer told ABCNews.com about bin Laden.
"I asked my CIA colleagues who have been on the hunt for him, and what surprised me was, no one was quite sure. Half assumed he was alive, and half assumed he was dead," Baer said. "Obviously, they have lost track of this guy completely."
Baer, who was the inspiration for the George Clooney character in the film "Syriana," said intelligence gathering in the mountainous region is "virtually impossible."
The warring Pashtun tribes along the border of Afghanistan and Pakistan complicate military operations in the region, and more troops won't help the U.S. capture bin Laden.
"It would take a million U.S. soldiers to go up there to subdue that area," Baer said.
Beyond the military fight along the border between Afghanistan and Pakistan, the CIA has for years engaged in an aerial war against suspected terrorist targets inside Pakistan using missile-armed Predator drones.
Since September, the CIA has substantially increased the number of those missile attacks, and some have successfully targeted senior al Qaeda operatives. But bin Laden remains an elusive target.
"If we did find bin Laden, it would be more out of luck than anything else," said Baer.
In late 2001, bin Laden was nearly captured in a battle with U.S. forces near Tora Bora, Afghanistan. However, the U.S. has since lost track of him, believing he is now hiding somewhere in the remote region around the Afghanistan and Pakistan border.
"Anyone familiar with the Afghan-Pakistan border area knows how rugged and inaccessible it is," CIA Director Gen. Michael Hayden said Thursday.