One of the most beloved American artists of the last century, Alexander Calder reimagined sculpture as an experiment in space and motion. He upended centuries-old notions that sculpture should be static, grounded, and dense by making artworks that often move freely, interacting with their surroundings. Calder’s ever-changing artworks invite a viewer’s sustained attention; over the course of many decades, The Museum of Modern Art provided a setting for this productive exchange.