Neutron halo nuclei

Experimental studies on neutron halo nuclei are reviewed. The recent development of radioactive nuclear beams enabled us to study detailed structure of nuclei far from the stability line. The neutron halos have been observed in nuclei near the neutron dripline by reaction measurements with intermediate- and high-energy radioactive nuclear beams. These nuclei are of a special interest in relation to shell structures near the dripline and to new excitation modes associated with the excess neutron on the nuclear surface.