Wavelength conversion devices are widely applied as ultraviolet-visible coherent light sources. This report provides information of the device, ranging from basic to advanced, as follows. First of all, characteristics of inorganic nonlinear optical materials used for wavelength conversion devices, and fundamental technical information such as the wavelength conversion scheme are provided. Secondly, several wavelength conversion devices utilizing those technologies are presented. Finally, the report ends by presenting recent examples of application of wavelength conversion devices to high output visible light sources and projection televisions.