Diode-pumped, solid-state laser sources started replacing gas and ion laser sources for commercial and laboratory applications about 10 years ago, and the trend is accelerating because of progress in two areas. First, more powerful, reliable laser diodes are available at lower cost, making diode-pumping not only attractive but also practical. Second, improvements in manufacturing have improved the quality while reducing the volume pricing for laser crystals such as Nd:YAG and Nd:YVO4 and nonlinear optical crystals such as b-BaB2O4 (BBO), LiB3O5 (LBO), KTiOPO4 (KTP). The nonlinear crystals are important because the fundamental output wavelength of Nd:YAG and Nd:YVO4 is near 1064 nm in the near-infrared, a wavelength that is extremely useful for many applications. However, if these lasers are to replace gas and ion lasers that emit in the visible and ultraviolet portions of the spectrum, they need some type of device that can shorten their wavelengths by doubling or tripling their frequencies. As the most powerful laser frequency conversion devices, nonlinear optical crystals are playing an increasingly important role in advanced laser technologies. The development of new crystals has combined with other laser technologies (diode pumping, ultrafast technologies and optical parametric processes) to greatly accelerate the creation of all-solid state lasers. Because of these changes, recently introduced laser sources have much shorter wavelengths (down to 187 nm), faster laser pulses (down to sub 10 fs), much wider tuning range (from 187 nm to 10 mm), higher powers and yet are considerably smaller than their predecessors.