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. “One of Calder’s objects is like the sea…,” wrote the philosopher Jean-Paul Sartre, “always beginning over again, always new.” 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.