In the analysis of plates and beams, in-plane velocities have been assumed to be small and negligible. This was nearly an unavoidable assumption due to the fact that the in-plane velocity was near impossible to determine accurately with conventional techniques. This assumption needs to be checked experimentally. In addition, general engineering structures, such as machines, TV towers, buildings, etc., have major in-plane motions that are actually out-of-plane motions as viewed from another vantage point. These also need to be measured. Now with the use of a Laser Doppler Vibrometer the development of a method to measure three-dimensional velocities has provided the ability to measure in-plane velocities accurately. This thesis outlines the methods used for such three-dimensional extraction and gives an example of its use. Not only is the final three-dimensional method described, but the whole process of developing the method is outlined. This will hopefully provide insight into the difficulties associated with this method as well as prevent other researchers from following similar fruitless approaches. / Master of Science