It took six years to plan, and four to build.
The wing showcases the institute's prized collection of 20th and 21st century art, architecture, design, and photography. It makes the art institute the nation's second largest art museum.
The wing was designed by award-winning international architect Renzo Piano.
"It's about openness. It's about accessibility. It's about lightness. It's about making a building that is not intimidating, a building that implies easy relationshio with the street and with the city," said Renzo Piano, Art Institute Modern Wing architect.
The public can celebrate as well, because admission to the entire museum is free through Friday, May 22.