A memorial was planned in the immediate aftermath of the attacks and destruction of the World Trade Center for the victims and those involved in rescue and recovery operations.

Arad worked with landscape-architecture firm Peter Walker and Partners on the design, creating a forest of swamp white oak trees with two square reflecting pools in the center marking where the Twin Towers stood.

[8] A dedication ceremony commemorating the tenth anniversary of the attacks was held at the memorial on September 11, 2011, and it opened to the public the following day.

The deciduous trees (swamp white oaks)[11] are arranged in rows and form informal clusters, clearings and groves.

New York City Mayor Michael Bloomberg replaced Whitehead as chair of the National September 11 Memorial & Museum.

Foundation executive committee chair Thomas S. Johnson said on May 9, 2006:The decision was made to not actively pursue new fund-raising efforts until complete clarity can be achieved with respect to the design and costs of the project.

Highlights included an exhibition of photographs, artifacts from the site, and a film with firsthand accounts from individuals who had directly experienced the attacks.

On October 19, 2011, William D. Shaddox of the National Park Service voiced concerns to the Senate Committee on Energy and Natural Resources about the agency's ability to provide the funds required by S.1537, testifying that NPS ownership of a property over which it would not have operational and administrative control (as stipulated by S.1537) was unprecedented.

The president of the memorial foundation said that family members were consulted and formed a consensus in favor of the design, and work would continue as planned.

[32] In 2006, at the request of Bloomberg and Governor George Pataki, builder Frank Sciame performed a month-long analysis that included input from victims' families, the lower Manhattan business and residential communities, architects and members of the memorial-competition jury.

Two 1-acre (4,000 m2) pools with the largest man-made waterfalls in the United States comprise the footprints of the Twin Towers, symbolizing the loss of life and the physical void left by the attacks.

The names are arranged according to an algorithm, creating "meaningful adjacencies" based on relationships—proximity at the time of the attacks, company or organization affiliations (for those working at the World Trade Center or the Pentagon) and in response to about 1,200 requests from family members.

"[56] In an August 29, 2011 Port Authority press release (after Hurricane Irene), Daniels said: "True to its name, the Survivor Tree is standing tall at the Memorial.

"[56] A Place of Remembrance: Official Book of the National September 11 Memorial describes the tree as "a reminder of the thousands of survivors who persevered after the attacks".

[62] In December 2010, the tree, then 30 feet (9.1 m) tall,[56] was returned to the World Trade Center site in a ceremony attended by Bloomberg, city officials[57] (including Parks and Recreation Commissioner Adrian Benepe and Port Authority executive director Chris Ward), survivors and rescue and recovery workers.

The path includes six large battered stones that, in the words of Michael Arad, "appear to jut up and out of the plaza as if violently displaced, and convey strength and resistance".

[66][67] The Sphere, a monumental cast bronze sculpture by German artist Fritz Koenig, was commissioned for the old World Trade Center and completed in 1971.

The committee stated that the Memorial's decision to not publish Arabic-language brochures violated HUD's Limited English Proficiency rules for grantees.

In December 2017, the ADC announced that the Memorial had signed a settlement agreement whereby its commemorative guide would be translated into Arabic and made available.

During the hour-long ceremony LaChanze sang "Amazing Grace", which she dedicated to her husband Calvin Gooding, who was killed in the World Trade Center attack.

[94] The pavilion has a deconstructivist design, resembling a partially collapsed building (mirroring the attacks), and houses two "tridents" from the Twin Towers.

[98] The Waterford Crystal "Hope for Healing" panels from the Times Square Ball for New Year's Eve 2002—which were inscribed with the names of emergency organizations and countries that had taken casualties in the attacks—were also donated to the museum's collection.

[102] Activists lobbied for the Museum to include a permanent exhibit about the neighborhood to "help the thousands of tourists who visit the site to understand that immigrants from Ottoman lands have played a patriotic role in the country's history,"[104][105] arguing that it was important to memorialize the multiethnic character of "Little Syria.

[108][109][110] When the museum opened to victim families and first responders on May 15, 2014, anger by some that it was profiting from souvenirs considered in poor taste was widely covered.

Family members objected to a party near unidentified remains; the sister of victim Robert Shay, Jr. tweeted, "Did you enjoy having drinks on top of my brother's grave last night?"

Shay and dozens of other visitors were angered that first responders were turned away from the museum the previous day while staff prepared for the party.

She said, "I am outraged that I can't visit my brother's final resting place without an appointment but people like Mike Bloomberg can wine and dine there whenever they want.

Among the latter was FDNY Lt. James McCaffrey, the brother-in-law of 9/11 victim and firefighter Orio Palmer, who called a ground-level tomb a more dignified location: "The decision to put the human remains of the 9/11 dead in this basement is inherently disrespectful and totally offensive."

McCaffrey said that the remains deserved a prominence equal to that of the Memorial's trees and pools, and that the ceremony was held early in the morning because of opposition to the decision.

Of the dispute over the proposed centers, one New York Times editorial argued that the IFC's opponents made trivial and unconvincing suggestions that both the IFC and the "cultural component" of architect Daniel Libeskind's plans would somehow diminish the scope of the Memorial Museum, and noted that the proposal for reducing the size of one of the centers had failed to consider the emotional impact of the space.