1.1 X-RAY DIFFRACTION SPECTROSCCOPY In the century since its birth, X-ray spectroscopy has come to define how material structures are quantified and understood. X-rays can probe the nanostructure of crystalline and amorphous materials with bond-length resolution and with minimum sample damage. These properties make X-ray spectroscopy fundamental to answering questions about bonding and nanoscopic order in hard crystalline, organic, and polymer materials. X-ray spectroscopy enabled landmark studies in materials science from the structure of metals and alloys 2 , our understanding of defects, the discovery of ferroelectric domains , quasicrystals , and the tetrahedral bonding of diamond . This success has resulted in many technological leaps, pushing the boundaries of structural quantification in materials. Synchrotron facilities have steadily advanced the temporal and spatial limits of X-ray spectroscopy with X-ray free electron lasers , nano-diffraction , coherent XRD imaging , and 4 th -generation beamlines facilities . At the same time, specialized laboratory diffractometers and beamlines have greatly increased options for high-throughput, in-situ, and operando experiments . However, despite the breakneck pace of recent technological developments, there has been little change to the foundations of X-ray spectroscopy since its invention.