The National September 11 Memorial & Museum (branded as 9/11 Memorial and 9/11 Memorial Museum) is the principal memorial and museum commemorating the September 11 attacks of 2001. The memorial is located at the World Trade Center site, on the former location of the Twin Towers destroyed during the attacks. The World Trade Center Memorial Foundation was renamed the National September 11 Memorial & Museum at the World Trade Center in 2007.
The winner of the World Trade Center Site Memorial Competition was Israeli-American architect Michael Arad of Handel Architects, a New York- and San Francisco-based firm. Arad worked with landscape architecture firm Peter Walker and Partners on the design which calls for a forest of trees with two square pools in the center, where the Twin Towers once stood.
In August 2006, the World Trade Center Memorial Foundation and the Port Authority of New York and New Jersey began heavy construction on the memorial and museum. The design is consistent with the original Daniel Libeskind master plan that called for the memorial to be 30 feet below street level (originally 70 feet) in a piazza. The design was the only finalist to throw out Libeskind's requirement that buildings overhang the footprints.
A memorial was planned in the immediate aftermath of the attacks and destruction of the World Trade Center to remember both the victims and those involved in rescue. The National September 11 Memorial & Museum at the World Trade Center is a non-profit corporation with the mission to raise funds for, program, own and operate the memorial and museum at the World Trade Center site. On September 11, 2011, a dedication ceremony was held at the memorial, commemorating the tenth anniversary of the attacks. The memorial officially opened to the public on September 12, 2011, while the museum will open one year later, on or around September 11, 2012. Three months after opening, the memorial has been seen by over 1 million visitors.
Source : en.wikipedia.org