Robert Benjamin Leighton (September 10, 1919 – March 9, 1997) was a prominent American experimental physicist who spent his professional career at the California Institute of Technology (Caltech). His work over the years spanned solid state physics, cosmic ray physics, the beginnings of modern particle physics, solar physics, the planets, infrared astronomy, and millimeter- and submillimeter-wave astronomy. In the latter four fields, his pioneering work opened up entirely new areas of research that subsequently developed into vigorous scientific communities.