For those who lost loved ones in these diabolical attacks, Wednesday may be particularly cruel, underscoring the realization that it is a year since they heard a certain laugh or a voice again or saw the familiar face of a loved one outside a photograph.
For others it may be another day in which they try to readjust after a horrific injury or emotional scar and move their spirit forward.
For all Americans it will be a time of sober reflection whether they go to "Ground Zero" in New York or the tiny village of Shanksville, Pa., or simply pause for a minute on their job to remember a day that many Americans think changed their lives forever.
In New York at "Ground Zero," the giant bunker where once stood the twin World Trade Center towers, the names of the 2,801 New York victims will be read aloud in alphabetical order, by former New York Mayor Rudolph Giuliani and a group of dignitaries including actor Robert DeNiro and Sen. Hillary Rodham Clinton, D-N.Y. The first ceremony there will begin at the moment the first plane hit, 8:46 a.m.
Many of the 191 people scheduled to read names in the ceremony are relatives of people who died in the attack.
It was the crash of two airliners into those towers that opened this nightmare for Americans. In addition to the thousands who died in the building, hundreds of rescue workers died after they entered the buildings, trying to save office workers.
In Washington, President George W. Bush and his wife, Laura, begin Sept. 11 at a church service near the White House, travel later to the Pentagon, where 189 Americans died and hundreds more were injured by a plane that dived into the building's western wall.
From Washington, the president will fly to the village of Shanksville, the final resting place of United Airlines Flight 93. It is on this aircraft that passengers, realizing what the hijackers were up to, tried to take over the plane and in doing so crashed it into a field. Forty-four died. It is believed this plane may have been headed for the U.S. Capitol and the passengers are credited with foiling this plot.
Finally, in the late afternoon on Wednesday, Bush arrives at "Ground Zero" in New York that has become history's recurring symbol of this tragedy. He may be joined by leaders of other nations who have traveled to New York for the opening session of the U.N. General Assembly.
Later, the president will address the nation (at 9 p.m. EDT) from Ellis Island in New York Harbor, where so many immigrants to the United States in the 19th and 20th centuries began their lives here.
Security will be tight in New York and Washington. Aircraft have been restricted in some areas and the Air Force is again flying a "fighter cap" over the two cities. The FBI has issued renewed warnings about Sept. 11 reporting that the "traffic" in threatening terrorist messages has increased. And the threat level has been bumped up from yellow to orange, one step below the most serious "red" level. But local and state authorities across the nation say that they are not planning increases in security.
Nearly 350 American towns and cities have also listed events to mark Sept. 11. Many of them focus on firefighters, with local ceremonies at firehouses to commemorate the firefighters, and police, who died in the World Trade Center.
"Amazing Grace" has been one of the more popular choices for music, played by orchestras and lone bagpipes.
Around the world, starting in New Zealand, choirs in different time zones are joining in a "Rolling Requiem," singing Mozart's Requiem at 8:46 a.m. local time in their time zones. The commemoration ends at Hawaii's Kawaiaha'o Church on Punchbowl Street in Honolulu.
Some 90 winners of the Medal of Honor will be in Shreveport, La., for a convention and will join city officials to pay homage to the Sept. 11 victims. Gen. Norman Schwarzkopf, of Gulf War renown, will be the speaker at their closing dinner Thursday.
In a number of states, mental health clinics will be fully staffed and open for counseling those facing the stress of Sept. 11. In Alaska AT&T will offer free long-distance calls to those wishing to contact friends or family living in the other 49 states.
In Des Moines, Iowa, a U.S. flag flown from a Musco Lighting Co. truck in recovery operations at both the WTC and the Pentagon will be presented. The company, which makes high intensity lighting equipment, is based in Oskaloosa, Iowa.
Church bells will ring, the names of victims will be read, National Guard troops will parade and there will be church services and concerts.
On a more light-hearted note the Bunker restaurant in Rochester, Wis., will host a "Burn bin Laden" party in the afternoon to torch a bin Laden effigy. This is the same restaurant that created an effigy of bin Laden during deer hunting season, slapped antlers on it and a sign that read "Open season. No tag required."
Chicago police officers and firefighters are being feted with a free dinner and show at Tommy Gun's Garage, a musical theater decked out as a 1920s speakeasy in the era of Al Capone.
Around the nation, others are marking the day with acts of kindness and giving. Blood drives are being held, people are being asked for donations of cans of food for the hungry and the outplacement firm of Challenger, Gray and Christmas Inc. in Chicago is using the lunch hour to raise funds for the Greater Chicago Food Depository, which feeds more than 310,000 people each year.