The use of X-rays of known wavelength to learn the structure of any crystalline material. Put otherwise, X-ray crystallography is a technology by which the locations of atoms in any crystal can be precisely mapped by looking at the image of the crystal under an X-ray beam.
... The crystal is placed in the beam of X-rays and the angles of diffraction of the X-rays are recorded as a series of spots on photographic film. This method (called the Laue method after the German physicist Max Theodor Felix von Laue) has been employed to determine and measure the physical structure of many materials.
One example of the use of X-ray crystallography has been our understanding of the structure and function of hemoglobin and its close relative, myoglobin. Hemoglobin is the protein that transports oxygen from the lungs to the tissues via red blood cells while myoglobin is its counterpart in muscle that stores oxygen and gives it up to muscle cells as needed.
In 1962 Max Perutz and John C. Kendrew from Cambridge University shared the Nobel Prize for Chemistry for their brilliant X-ray diffraction analyses of hemoglobin (Perutz) and myoglobin (Kendrew).