KTiOPO4 (KTP) satisfies many of the criteria required of a second harmonic generating (SHG) material. KTP combines large nonlinear optical coefficients with broad spectral, temperature, and angular bandwidths. It is also chemically inert and easy to fabricate. Accordingly it has been called the material of choice for the doubling of 1.064 μm Nd:YAG radiation. A history of the development of KTP to its present status is presented with special emphasis on crystal growth and SHG performance. A summary of various physical, chemical, crystallographic, dielectric, ferroelectric, and optical properties of the material are given. Applications such as SHG of KTP under conditions of noncritical phase matching, optical parametric oscillation, blue light generation via wave mixing, and guided wave optics are discussed. The future of KTP as a nonlinear optical material is addressed stressing solutions to crystal size limitations and bulk damage problems.