The new wing took six years to plan and four to build. It showcases a leading collection of 20th and 21st century art, architecture, design, and photography and 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 relationship with the street and with the city," Piano said.
To help celebrate the wing, admission to the entire museum is free through Friday.