X-ray phase contrast (PC) imaging is a measurement technique dealing with the intensity of X-band radiation. According to this technique the X-ray wave detection is organized so that the measured intensity (image) depends on the wave phase. The simplest PC setup includes an X-ray source, a device or medium necessary for generation of PC and detector. Physical models describing PC image formation process are usually available. Under certain conditions one can solve an inverse problem (which is often ill-posed) and relate PC image to properties of an X-ray source or use PC for projection or tomography imaging of various objects. In the talk we consider two PC techniques and, correspondingly, two different applications. First, we discuss an application of a propagation-based PC to the soft X-ray spectroscopy of ultrafast laser-driven sources and free-electron lasers. Second, we consider an analyzer-based PC technique and its application to the hard X-ray index of refraction tomography of large, strongly absorbing objects.