The first unambiguous experimental detection of ion plasma waves is reported. These short-wavelength ({ital k}{lambda}{sub De}{gt}1), purely electrostatic ion waves were first predicted by Tonks and Langmuir in 1929. The waves are observed in a long-scalelength ({ital L}{gt}10{sup 4}/{ital k}), multiply ionized ({ital Z}=22), laser-produced plasma. The frequency ({omega}), wave number ({ital k}), and amplitude evolution of the ion waves are measured by time-resolved spectroscopy of the scattering from the ion waves of a probe laser beam. The wave frequency is approximately the ion plasma frequency ({omega}{sub {ital pi}}) when {ital k}{lambda}{sub De} exceeds 1, as predicted by the theoretical dispersion relation.