Although a number of calculations of the inner potential have been made in the past for various crystals, the results have not been entirely satisfactory, and in some cases widely divergent values for the same substance were published by different authors. In the present work, a number of these calculations are examined and possible sources of error discussed. It is shown that electron distribution charts and curves obtained experimentally are not suitable for the calculation of inner potential, and an exponential approximation for atomic scattering factors is given which is found to be more reliable for this purpose. A simple modification of the electron distribution curves obtained from these atomic scattering factors is described; this is applied when the atoms are bound in a crystal lattice, thus enabling the inner potential of the crystal to be calculated. The results of a number of calculations based on this method are given and compared with the experimental values, the agreement being satisfactory.