One World Trade Center is officially open for business. According to a New York Times report publishing company Condé Nast moved employees into the building on Monday, becoming its first tenant.

Planning for the building, referred to as the Freedom Tower until 2009, began shortly after the terrorist attacks on the twin towers in 2001. By 2005 planners revealed the official design for the building.

Led by the Port Authority of New York & New Jersey, construction for One World Trade Center began in 2006 and took nearly eight years. Lessons from the 2001 terrorist attacks have been incorporated into the building’s design. According to Silverstein Properties, the real estate company that owns the lease for the World Trade Center site, One World Trade Center has fireproofing, biochemical filters, and multiple backup emergency lights in excess of what New York City building codes require. The building also has extra-wide stairs and exits designed with evacuation in mind.

“Lower Manhattan is poised to become one of the world’s most sought-after central business districts,” said Scott Rechler, vice chairman of the Port Authority of New York & New Jersey. “This would have been hard to predict in the aftermath of the tragedy of 9/11.”

At 1,776 feet, One World Trade Center is the tallest building in the U.S. The office tower is located in the World Trade Center complex in Manhattan, near where the twin towers stood before September 11, 2001. The building is 104 stories tall and has three million square feet of space including offices, a sprawling lobby, and an observation deck.

Two more office towers are currently planned for the World Trade Center complex. Just last week Siverstein Properties announced that $1.6 billion in funding had been secured for Three World Trade Center, an 80-story skyscraper that will be located on Greenwich Street in Manhattan. The building is expected to be completed in 2018 and advertising media company GroupM has already signed on as a tenant.