Silver gallium sulfide (AgGaS2), silver gallium selenide (AgGaSe2), and silver gallium indium selenide (AgGaxIn(1 − x)Se2) are unique nonlinear crystals suitable for a wide range of three-wave mixing applications. They combine strong nonlinear coupling with phase matching across a wide (0.5 − 12.5 μm) transmission range. These properties provide the basis for CO2 laser harmonic-generator (HG), visible (VIS), and near-infrared (NIR) pumped opticalparametric-oscillator (OPO) and sumand difference-frequency-generator (SFG/DFG) systems for producing tunable laser radiation from approximately 0.65 to 12 μm. A wide range of pump lasers is now available, including diode lasers capable of direct pumping of AgGaS2 and efficient diode-pumped lasers for pumping any of these crystals. Significant progress in material characteristics and nonlinear optical (NLO) performance has been accomplished. Bulk absorption for production-quality AgGaS2 is ~0.01 − 0.02 cm across the 0.8−9-μm region. Exceptional crystals of AgGaS2 have absorption <0.0005 cm−1 at 1.064 μm, and even at 0.633 μm, absorption is ~0.015 cm−1. Figure 1 illustrates the late 1980s vintage and present transmission of AgGaS2. For AgGaSe2, absorption for production material ranges from 0.010 cm to 0.018 cm−1 from 1 μm to 11 μm. Certain crystals can have 0.007−0.008 cm−1 absorption at 10.6 μm. The NIR transmission curves for AgGaSe2 and AgGaxIn(1 − x)Se2 appear in Figure 2. This combination of optical properties, along with their good physical characteristics, make these two crystals versatile for NLO applications spanning the VIS to the infrared (ir).