The Fizeau Wavemeter is a real-time laser-wavelength measuring instrument intended for use with either pulsed or cw lasers. The instrument contains a static Fizeau interferometer which is illuniinated by the laser. The fringe pattern of the interferometer is sampled by a 1024 element photodiode array and analyzed by a small computer to determine the wavelength of the illuminating laser. An earlier version of the instrumentl demonstrated a resolution of 10 -7 (about 50 MHz in the visible) at a read-out rate of 15 Hz, but suffered from systematic drifts in the calibration. Recent modifications in the software 2 and in the optical system have virtually eliminated. sensitivity to fringe amplitude non-uniformity and to wavefront curvature. Temperature sensitivity has been reduced to a level commensurate with the coefficient of thermal expansion of the interferometer spacer.