The emergence of robots as essential components in the development of flexible manufacturing systems has created a demand for measurement techniques capable of measuring their performance. Typically it is required to measure the position of the robot end effector at speeds of up to 5 m/sec in a 1 metre sided cube and with a precision better than 0.1 mm. An instrument has been developed that uses a laser tracking technique and the principle of triangulation to determine the x,y and z co-ordinates of an optical target. It consists of two identical sub-systems, a retroreflective cat's eye target and a supervisory microcomputer. Each sub-system aims a low power laser beam at the target and detects the retroreflected beam for feedback to the mirror actuators controlling the beam direction. The instrument has been modelled, calibrated and evaluated. The effect on the target coordinate calculation of various system errors has been studied and a variety of measurement tools and methods are presented to calibrate the instrument both at component and sub-system level and also as a final system. The design of the cat's eye target is reviewed and a method of manufacture presented. Preliminary results and design details of a new optical sub-system with up-graded characteristics are also included. Tests show that the present instrument has a measurement accuracy of 0.03%, a repeatability of 0.01% (all for 1 standard deviation) for a measurement space of approximately one metre cube. The beam steering scanners have a bandwidth in excess of 74 Hz and the tracking velocity is approximately 3 m/s.