A technique to determine the three-dimensional velocity of a point on a vibrating structure is developed. This technique uses a reference-beam type laser-doppler velocimeter in three independent positions to determine the target velocity in a non orthogonal coordinate system. The transformation from non-orthogonal to orthogonal coordinate systems is analyzed. The sensitivities of the resulting velocity to measurement noise and position errors are also analyzed. Recommendations are made for future testing and applications of this technique.