The frequency of an external-cavity diode laser has been stabilized to absorption lines of water vapor at wavelengths around 944 nm. The primary application of this stabilized laser is to provide a frequency reference for differential absorption lidar measurements of atmospheric water vapor. A wavelength modulation technique is used to provide derivative-like error signals for a control loop to continuously tune the laser to line center. The design of the stabilization scheme is provided including the optical layout and feedback loop. Spectroscopic data are presented on several different absorption lines, showing the derivative-like signals used for stabilization. Results of the stabilization show the laser frequency locked to within 10 MHz of absorption line center, well within the precision needed for lidar applications. © 2001 Society of Photo-Optical Instrumentation Engineers.