Crystallography - the study of crystals, their structures and properties, plays an important role in a wide range of disciplines, including biology, chemistry, materials science and technology, mineralogy and physics, as well as engineering. The scientific breakthroughs in the first half of the 20th century, leading to applications as diverse as nuclear power and semiconductor technology, were built, to a considerable extent, upon detailed understanding of metallic and inorganic crystal structures. In the latter half of the 20th century, molecular biology, founded upon the determination of molecular crystal structures, has led to a deep-rooted change in medicine, with the structures of biologically important molecules such as insulin, the epoch making determination of the crystal structure of DNA and recent studies of protein structures, being pivotal.