We have designed and constructed a new Compact Cloud and Aerosol Lidar (ComCAL) for atmospheric research in the troposphere. The main features of this lidar system are as follows: A Nd:YAG Laser (Quantel Brilliant) emits laser pulses at 1064 nm, 532 nm, and 355 nm vertically into the atmosphere with a repitition rate of 20 Hz. In order to reduce the divergence the beam is expanded fivefold of its original diameter. The backscattered light is collected by a telescope in a Newtonian configuration and 40 cm aperture. The sending and emitting optics including the laser head are all mounted to one rigid, actively temperature stabilized frame in order to achieve maximum stability of the system and to avoid the necessity of realignment even under difficult conditions.