Summary Spatial Light Modulator (SLM) systems for phase modulation of coherent light sources are mainly MEMS- (Micro-Electro-Mechanical Systems) or LCD- (Liquid Crystal Display) based. Driving forces for this technology are mainly the consumer electronics industry leading to high-resolution reflective micro-displays. These days panels with 1920 × 1200 pixel are available. The pixel pitch goes down to 8 microns, the devices can handle also high power applications and show an almost analogue modulation of the light either in amplitude or phase. The phase modulating properties of these devices enable a light efficient optical reconstruction of digital holographic data or active wave front control.