Hall B is the smallest of Jefferson Lab's three experimental halls. It is 98 feet in diameter and 65 feet from floor to ceiling. It is equipped with the CEBAF Large Acceptance Spectrometer, or CLAS, which is shaped like an elongated sphere. Experiments in this hall can receive electron beam or a photon beam. A major research program in Hall B has been the investigation of the quark-gluon structure of protons and neutrons and a detailed study of excited states.