The theory of solid state Yb:YAG thin disk laser is introduced and it is compared with traditional rod Nd:YAG lasers. The powerful function of VersaDisk laser as dual wavelength output, wavelength tuning ability and single frequency are illustrated. Its scientific applications as high-resolution spectroscopy in the NIR, Bose-Einstein condensates and laser tweezers, high CW power Ti:sapphire and dye laser pumping are introduced.