The Adiabatic Toroidal Compressor (ATC) is being built to investigate the feasibility of a proposed technique for increasing the density and ion temperature of conventional tokamaks. By applying a suitable magnetic field normal to the plane of a usual tokamak discharge, the major radius is caused to shrink to about 0.4 of its original value, thereby resulting in an increase both in temperature and density. The experiment is important because, if successful, the technique could be applied to achieve plasma temperatures and densities significantly greater than otherwise obtainable in a given size facility. Selection of the machine size, field strength and time scale for the operating cycle was based both on the desire to achieve values of temperature and density well exceeding those already reported by others and on the conviction that experimental results should be forthcoming by mid-1972 to be useful in the design of larger experimental facilities. The first goal is expected to be met in the choice of a field strength of 50 kG at 37 cm major radius, the location of the 241 kA discharge after compression. The second goal required the use of presently available (or readily constructed) power supplies and an amount of engineering manpower consistent with existing laboratory programs. Buildup of the initial discharge within about 5 ms, a thermalizing time of up to 20 ms, and a compression time of about 2 ms are attainable within the above framework and are consistent with the energy replacement time of the plasma.