A presentation of a preliminary model atmosphere for an altitude region between 100 and 800 km. The scientific results obtained from rockets as well as from satellites are used to determine the variation of density with altitude. The pressure and scale height are calculated from the density. The experimental and theoretical results are shown in the form of graphs and tables. Because of solar effects these physical parameters may vary by a factor of two or more, which is approximately the average uncertainty involved in evaluating the experimental data.