The ARIES research program is a multi-institutional effort to develop several visions of tokamak reactors with enhanced economic, safety, and environmental features. Three ARIES visions are currently planned for the ARIES program. The ARIES-I design is a DT-burning reactor based on “modest” extrapolations from the present tokamak physics database and relies on either existing technology or technology for which trends are already in place, often in programs outside fusion; ARIES-II is a DT-burning reactor which will employ potential advances in physics; and ARIES-III is a conceptual D-3He reactor. The first design to be completed is ARIES-I, a 1000 MWe power reactor. The key features of ARIES-I are: (1) a passively safe and low environmental impact design because of choice of low activation material throughout the fusion power core, (2) an acceptable cost of electricity, (3) a plasma with performance as close as possible to present-day experimental achievements, (4) a high performance, low activation, SiC composite blanket cooled by He, and (5) an advanced Rankine power cycle as planned for near term coal-fired plants. The reactor major radius is 6.75 m, the plasma minor radius is 1.5 m, the average neutron wall loading is 2.5 MW/m2, and the mass power density is about 100 kWe/tonne of fusion power core. The design uses moderately high plasma aspect ratio (A ≡ 1/ɛ = 4.5), low plasma current (Ip = 10 MA), and high magnetic field (∼ 11 T at the plasma center). Steady-state operation is presumed, based upon ICRF fast-wave current drive to supplement a large (68%), theoretically predicted bootstrap current. Impurity control and particle exhaust are based on high-recycling poloidal divertors in a double-null configuration. Self-consistent core and scrape-off-layer calculations predict τα/τE of 4 and an alpha exhaust efficiency of 50 %, both sufficient for steady plasma burn. The maximum field at the coil is 21 T. It is found that the maximum stress in the structural material of the magnets is about 700 MPa and the industrially available alloys can be used. The blanket and shield are to be constructed of silicon-carbide (SiC) composite material, and cooled by helium at 10 MPa. The structure has a very low level of induced activation, permitting the design to be passively safe, particularly if lithium dioxide or lithium orthosilicate can be used as the tritium breeding material. Radioactive waste would meet the U. S. criteria for shallow-land burial. The cost of electricity is projected to be 65 mill/kWh (in constant 1988-dollars), comparable to projections for advanced fission and coal-fired plants using the same costing basis. The ARIES-I research has also identified key physics and technology areas with the highest leverage for achieving attractive fusion power system.