Due to high attendance and overflowing collections, the museum announced in October 2006 that Frank Gehry would design a building expansion.
The 80,000-square-foot (7,400 m²) gallery will be built entirely underground behind the east entrance stairs and will not alter any of the museum's existing Greek revival facade.
The construction was initially projected to last a decade and cost $500 million.
It will increase the museum's available display space by sixty percent and house mostly contemporary sculpture, Asian art, and special exhibitions.

Uncertainty was cast on the plans by the 2008 death of Anne d'Harnoncourt, but new director Timothy Rub, who had initiated a $350 million expansion at the Cleveland Museum of Art, will be carrying out the plans as scheduled.
 In 2010, Gehry attended the groundbreaking for the second phase of the expansion, due to be completed in 2012.
 In that phase, a new art handling facility was created on the south side of the building, enabling the museum to reclaim a street level entrance, closed since the mid-1970s, which leads to a 640-foot (200 m)-long vaulted walkway that extends across the museum and is original to the 1928 building.
The north entrance will be reopened to the public as a part of the "core project", which is scheduled for completion in 2020.
The core project also focuses on the interior of the current building and will add 90,000 square feet (8,400 m²) of public space, including 11,500 square feet (1,070 m²) of new gallery space for American art and contemporary art.
 In addition, a new space called the forum will be created, along with dining and retail spaces.
Said Gehry: "When it's done, people coming to this museum will have an experience that's as big as Bilbao.
It won't be apparent from the outside, but it will knock their socks off inside."

In March 2017 the museum announced a $525 million campaign.
The core project is budgeted at $196 million and will be funded through the campaign.
The museum also announced that more than 62 percent of the campaign goal has been met, as of March 30, 2017.

The most controversial part of the Gehry design remains a proposed window and amphitheater to be cut into the east entrance stairs.
Others have criticized the design as too tame.
The Gehry expansion is projected to be completed by 2028.
Due to high attendance and overflowing collections, the museum announced in October 2006 that Frank Gehry would design a building expansion. The 80,000-square-foot (7,400 m²) gallery will be built entirely underground behind the east entrance stairs and will not alter any of the museum's existing Greek revival facade. The construction was initially projected to last a decade and cost $500 million. It will increase the museum's available display space by sixty percent and house mostly contemporary sculpture, Asian art, and special exhibitions.
Uncertainty was cast on the plans by the 2008 death of Anne d'Harnoncourt, but new director Timothy Rub, who had initiated a $350 million expansion at the Cleveland Museum of Art, will be carrying out the plans as scheduled.  In 2010, Gehry attended the groundbreaking for the second phase of the expansion, due to be completed in 2012.  In that phase, a new art handling facility was created on the south side of the building, enabling the museum to reclaim a street level entrance, closed since the mid-1970s, which leads to a 640-foot (200 m)-long vaulted walkway that extends across the museum and is original to the 1928 building. The north entrance will be reopened to the public as a part of the "core project", which is scheduled for completion in 2020. The core project also focuses on the interior of the current building and will add 90,000 square feet (8,400 m²) of public space, including 11,500 square feet (1,070 m²) of new gallery space for American art and contemporary art.  In addition, a new space called the forum will be created, along with dining and retail spaces. Said Gehry: "When it's done, people coming to this museum will have an experience that's as big as Bilbao. It won't be apparent from the outside, but it will knock their socks off inside."
In March 2017 the museum announced a $525 million campaign. The core project is budgeted at $196 million and will be funded through the campaign. The museum also announced that more than 62 percent of the campaign goal has been met, as of March 30, 2017.
The most controversial part of the Gehry design remains a proposed window and amphitheater to be cut into the east entrance stairs. Others have criticized the design as too tame. The Gehry expansion is projected to be completed by 2028.
Philadelphia Museum of Art