The paper begins with the work of various pioneers in the use of the optical spark up to the early 1920s. These include Fox Talbot, Mach, Cranz, Boyes, Worthington and Bull amongst others. Mention is made of some of their ingenious solutions for problems of triggering and the problems to which they applied spark photography. These efforts began with single exposures and gradually turned to various multiple spark systems in order to incorporate a time history into their observations. There follows descriptions of spark source types, their backing circuitry, optical properties, general usage, later advances and applications including their use in aeroballistic ranges. Finally spark source advantages and disadvantages are compared.