The Advanced Toroidal Facility (ATF), now under construction at Oak Ridge National Laboratory, will be the world's largest stellarator experiment when it begins operation in early 1987. It will have a 2.1-m major radius and a 0.3-m average plasma radius, a magnetic field capability of up to 2 T for a 5-s pulse and up to 1 T steady state, and up to 5 MW of plasma heating. The ATF is designed to study a wide range of toroidal confinement issues, including confinement and stability of high-beta plasmas, low-collisionality transport, impurity behavior, magnetic configuration optimization, and steady-state operation. The ATF is the result of a study of a large number of possible coil configurations. It is an 1 = 2, 12-field-period torsatron with rotational transform between 0.3 and 1 and a plasma aspect ratio of R/ā = 7. This optimized helical field coil configuration permits direct access to a high-beta, second stability region in a flux-conserving manner, and volume-average beta values >8% may be achieved. The poloidal coil system allows study of a large variety of stellarator configurations, including those with a helical magnetic axis, and external control of the fundamental magnetic configuration parameters, including rotational transform, shear, magnetic well, and plasma shape. The ATF consists of two segmented, jointed helical field coils; three sets of poloidal field coils; a thin, helically contoured vacuum vessel; and a thick, segmented, toroidal shell support structure. Its important design features include extensive access for plasma heating and diagnostics, a high degree of construction accuracy, and parallel construction techniques. A description of the ATF torsatron, the physics and engineering reasons for the different design choices, and the expected capabilities of the device are presented.