Scientific experiments which interact two or more short-duration events must synchronize them in time. Laser and X-ray light sources can now produce pulses with few-femtosecond (1 femtosecond = 0.00000000000001 seconds) or sub-femtosecond duration, requiring precise timing. It is possible to measure and control the timing of lasers with this precision, using stable RF and optical frequencies transmitted over fiber optics. A combination of optical and electronic technology has been developed to support short pulse X-ray and optical science at large user facilities.