Alexander Calder was an American sculptor who is best known for his innovative mobiles (kinetic sculptures powered by motors or air currents) that embrace chance in their aesthetic and his monumental public sculptures. It was the mixture of his experiments to develop purely abstract sculpture following his visit with Mondrian that led to his first truly kinetic sculptures, manipulated by means of cranks and motors, that would become his signature artworks. Calder’s kinetic sculptures are regarded as being amongst the earliest manifestations of an art that consciously departed from the traditional notion of the art work as a static object and integrated the ideas of gesture and immateriality as aesthetic factors. Dating from 1931, Calder’s sculptures of discrete movable parts powered by motors were christened “mobiles” by Marcel Duchamp, a French pun meaning both “motion” and “motive.” However, Calder found that the motorized works sometimes became monotonous in their prescribed movements. His solution, arrived at by 1932, was hanging sculptures that derived their motion from touch or air currents. They were followed in 1934 by outdoor pieces which were set in motion by the open air. The wind mobiles featured abstract shapes delicately balanced on pivoting rods that moved with the slightest current of air, allowing for a freer, more natural, shifting play of forms and spatial relationships. At the same time, Calder was also experimenting with self-supporting, static, abstract sculptures, dubbed “stabiles” by Jean Arp in 1932 to differentiate them from mobiles. In the 1950s, Calder increasingly concentrated his efforts on producing monumental sculptures (his self-described period of “agrandissements”), particularly as public commissions increasingly came his way in the 1960s.