Potassium titanyl phosphate (KTP) is a unique nonlinear optical material that is being widely used for second harmonic generation of Nd lasers emitting around 1 μm. KTP is also very attractive for various sum and difference frequency and optical parametric applications over its entire transparency range from 0.35 to 4.5 μm. Its combination of large electrooptic coefficients and low dielectric constants make KTP potentially useful for various electrooptic applications. Low loss optical waveguides can be formed in KTP and several electrooptic and nonlinear optic devices have been fabricated. Potassium titanyl arsenate (KTA), which is isostructural with KTP has recently been grown and characterized. Initial results show that KTA has nonlinear optic and electrooptic properties that are superior to KTP.