Abstract: The pioneering contributions to X－ray astronomy made by Riccaedo Giacconi who won the 2002 Nobel Prize for Physics are described, with emphasis on his extensive observations of the X－ray universe and development of X－ray imaging. The relationship between the advancement of astrophysics and the development of X－ray space observation is pointed out. The concepts of universal dark matter, binary accretion and X－ray jets are also presented. Finally, the outlook for high energy astrophysics is discussed.