X-ray crystallography is a scientific technique used to determine the atomic and molecular structure of a crystal. By directing X-rays at a crystal, the rays are scattered by the atoms within, creating a pattern that can be analyzed. This pattern reveals the arrangement of atoms in the crystal, allowing scientists to understand the material's structure. This method is widely used in various fields, including chemistry, biology, and materials science. It has been instrumental in discovering the structures of important molecules, such as DNA and many proteins, aiding in advancements in drug design and other applications.