Abstract: The basic concepts, physical pictures and techniques used in the development of X-ray phase contrast imaging are expounded, including the wave and corpuscular dual properties of light, the concept of phase, and the coherence of conventional and synchrotron radiation X-ray sources. The methods of X-ray phase contrast imaging, the basic principle of 3D imaging, and the latest progress of phase contrast imaging are also discussed. For a better understanding of the progress in this innovative new technique the rather abstract concepts of the first order and second order derivatives of phase are related to the displacement, the tilting and bending distortion of the wave front of the propagating light.