X-ray crystallography is a way to see the three-dimensional structure of a molecule. The electron cloud of an atom bends the X-rays slightly. This makes a "picture" of the molecule that can be seen on a screen. It can be used for both organic and inorganic molecules. The sample is not destroyed in the process.
The technique was jointly invented by Sir William Bragg (1862–1942) and his son Sir Lawrence Bragg (1890–1971). They won the Nobel Prize in Physics for 1915. Lawrence Bragg is the youngest to be made a Nobel Laureate. He was the Director of the Cavendish Laboratory, Cambridge University, when the discovery of the structure of DNA was made by James D. Watson and Francis Crick in February 1953.
The oldest method of X-ray crystallography is X-ray diffraction (XRD). X-rays are fired at a single crystal and the way they are scattered produces a pattern. These patterns are used to work out the arrangement of atoms inside the crystal.