The principle of the EDE method is to use a bent crystal monochromator to focus a polychromatic beam on the sample. The beam passing through the sample then diverges towards a position sensitive detector where beam position is correlated to energy.

The dispersive configuration of XAS has two main advantages that make it scientifically attractive. First, the whole X-ray absorption spectrum is collected simultaneously which makes the technique especially useful for the study of fast processes. Second, the size of the focussed beam at the sample position is small and very stable due to the fact that no movement of optical elements is required to collect the spectral data.