This is the first of two special issues of Optical Engineering on optical techniques in experimental mechanics, which I have been kindly asked by Dr. Caulfield to organize. The first issue deals with coherent optical methods, and the second with incoherent optical methods. The division is somewhat arbitrary because many light sources are partially coherent and some methods require the use of both coherent and incoherent light sources. In essence, I have called a method a coherent optical technique if a laser is used as the primary information gathering device and if, in the process, some sort of the coherent property of the light is utilized. Otherwise, it is classified as an incoherent optical technique.