Professor Billinge has dedicated his life to finding and characterizing local structures, local distortions and hidden symmetries in materials. It all started with an undergrad in Metallurgy and Materials Science at Oxford University, then a PhD at University of Pennsylvania. This led to an interest in the physics of materials and the physics of scattering and a 13 year stint in a Physics and Astronomy Department at Michigan State University. Since 2008 he has been in his current position at Columbia University, with an additional 14 year joint appointment at Brookhaven National Laboratory. He is best known for his contributions to the development of the PDF method, the topic of this book, into a powerful modern materials characterization tool. Kirsten M. Ø. Jensen's undergraduate and PhD studies were both completed at Aarhus University in Denmark, graduating in 2013. She was at this point already very interested in structure/property relations in nanoscale materials, and after her PhD, she joined Prof. Billinge's group at Columbia University for a postdoctoral fellowship. She has been at University of Copenhagen since 2015 where she leads her research group. She is known for her innovative application of x-ray scattering methods, and especially PDF analysis, to problems in nanomaterials chemistry.