Copies of letters written to Charlotte Moore Sitterly, David R. Lide, and E. U. Condon from Niels Bohr, Samuel Goudsmit, Arthur Schawlow, Gerhard Herzberg, I. I. Rabi, and Linus Pauling about Moore's published three-volume work on Atomic Energy Levels. Schawlow's letter also discusses the development of the laser and how it would have been impossible without the information the National Bureau of Standards published about energy levels of atoms. Pauling's asks for additional information to make further calculations with.