Abstract: A laser velocimetry technique for the measurement of the three dimensional components of velocity of a particle in a fluid flow has been described. It is based on the use of a measurement region consisting of two optical probe volumes. The two optical probe volumes are physically separate and each consists of an optical fringe pattern formed by the interference of two coherent beams of the same wavelength. Two of the components of velocity are determined experimentally from the doppler signals arising from the frequency change of light scattered from a particle suspended in the fluid flow as it passes through probe volumes. The third component of velocity is derived from measuring the time of flight of a particle in the fluid flow as it passes from the center of one probe volume to another probe volume.