Studies of atomic spectra extend back to the Fabry–Perot interferometer. This chapter describes the history and measurement of radiation correction effects—the Lamb shift. It also describes contributions to laser spectroscopy. The chapter provides a review of work with emphasis on the more activities. In addition to the Fabry–Perot interferometer already outlined it is worth noting applications of Fourier transform spectrometry to larger structures, example measurements in mercury by S. Gerstenkorn et al and bismuth by S. George et al. In 1961 D. J. Bradley described one of the applications of a photoelectric spectrometer to isotope shift and demonstrated the rapid measurement of isotopic abundance in mercury. Much interferometric work on atomic structures was carried out in Germany in the 1930s and 1940s. F. A. Korolyov and V. I. Odintsov studied line widths in an atomic beam of helium and the effects of electron impact excitation; Stanley described an atomic beam source for the rare gases.