Various X-ray fluorescence spectrometers are now commercially available, and these spectrometers are classified into two categories, i.e., energy dispersive and wavelength dispersive (Table 1). Energy dispersive instruments are of low resolution. Wavelength dispersive instruments are often referred to as high resolution. However, commercially available wavelength dispersive instruments are usually equipped with a one-crystal dispersion unit. Therefore, to be more precise, these instruments could be called medium resolution apparatuses. There are other types of spectrometers which are two- or three-crysral spectrometers, and which are known to have very high resolving power. High resolution X-ray fluorescence spectrometers, however, have rarely been constructed. This is because this type of spectrometer needs a very precise and complicated scanning mechanism, and also because the intensity of X-ray fluorescence is often lost.