The diffraction of X-rays by crystals is the principal tool for the study of the atomic and molecular structure of matter. Thanks to this technique we are able to understand the molecules of medicines, minerals, and synthetic and natural materials, and also the structure of the macromolecules that are integral to life: nucleic acids, proteins and carbohydrates. This information helps us to understand how, for example, medicines work and how to improve them. Would you like to know what the fundamentals of diffraction are? Have you heard about the large synchrotron facilities? Do you know how an antibiotic is designed?