Twenty-two notebooks contain the main theoretical research done by Fermi during the period 1926-1937. They include Fermi statistics, the atomic model of Thomas-Fermi, the theory of hyperfine structure and many other spectroscopic phenomena such as the Raman effect in gases and crystals, the intensity of spectral lines of alkalines and the theory of beta decay of radio-active bodies. A few of the notebooks also contain the manuscript of Fermi's formulation of quantum electrodynamics which was later published. Ten additional notebooks (1934-1938) are "registri" of experimental data on artificial radioactivity.