Laser interferometry has rapidly moved from the research phase to practical application in the laboratory and factory. Principal uses are for measuring lengths or coordinates of objects to superior accuracy and for measuring parameters or quality of optical components or systems. The long coherence length of the laser source and its high intensity are principal advantages but they also lead to confusing multiple fringe patterns. A laser interferometer has been used to measure the radii of surfaces and to position the elements of high quality lenses so that they are centered and spaced to high accuracy. A polarization system is used to eliminate unwanted fringe patterns and balance intensities in the arms of the interferometer. I have been asked to talk about laser interferometry, a topic that has been extensively discussed in the past few years. I am sure however, that you have all heard that laser beams can be coherent over many miles and at the same time can have more than enough intensity for almost any type of interferometry. The predictions for applications have been impressive and they are coming true. I believe that the practical realities of the use of the laser in interferometry can be better considered in terms of actual applications since the real growth of the field is the total of many small almost independent uses. I will therefore describe an application that I am familiar with - the use of laser interferometry in the assembly of very precise lenses for use in making integrated circuit masks.