A laser ceilometer is an optical radar system which ascertains the height of the base of cloud by measuring the time taken for a pulse of light to travel from the transmitter to the cloud base and to return to the receiver. The single field unit houses the GaAs laser optical transmitter, optical receiver and the signal detection and processing electronics. The height of the base of the cloud is processed digitally within the field unit. The equipment has been designed to overcome the various limitations of earlier ceilometers, such as the base-line requirement, moving mechanical parts, dangers from high-powered lasers and constant maintenance to ensure alignment. Proven modern technology is employed throughout. The range of cloud-base heights over which the equipment operates is 30–1455 m. The equipment is modular, thus greatly easing maintenance. Theoretical considerations and constructional details will be discussed. The ceilometer has been compared at an airport with a cloud-base recorder operated by the British Meteorological Office. The ceilometer worked well within its specification in this operational environment, and these results will be presented