An optical laser slope gage was successfully constructed, calibrated , and tested for the measurement of the instantaneous wave slope in a two-dimensional wave tank. The operation and calibration was established, based on the refraction of a light beam at the air-water interface. The wave elevation time series obtained from the integrated slope showed good agreement with the measurements obtained from a conventional wave probe. Preliminary measurements on a dual component wave have also shown this device useful for obtaining important information on wave-wave interactions.[gravityform id=”2″ title=”true” description=”true”]