The Salt River (Spanish: Río Salado, O'odham [Pima]: Onk Akimel, Yavapai: Hakanyacha or Hakathi:, Maricopa language: Va Shly'ay) is a river in Gila and Maricopa counties in Arizona, United States, that is the largest tributary of the Gila River. The river is about 200 miles (320 km) long. Its drainage basin covers about 13,700 square miles (35,000 km²). The longest of the Salt River's many tributaries is the 195-mile (314 km) Verde River. The Salt's headwaters tributaries, the Black River and East Fork, increase the river's total length to about 300 miles (480 km). The name Salt River comes from the river's course over large salt deposits shortly after the merging of the White and Black Rivers.

According to the Geographic Names Information System, the Salt River has also been known as:

The Salt River is formed by the confluence of the White River and the Black River in the White Mountains of eastern Gila County. The White and Black rivers, and other tributaries of the upper Salt River, drain the region between the Mogollon Rim in the north and the Natanes Mountains and Natanes Plateau to the east and south. Tributaries of the Salt River also drain the Sierra Ancha and Mazatzal Mountains. The White and Black rivers drain the White Mountains in the Fort Apache Indian Reservation. Together the two rivers drain an area of about 1,900 square miles (4,900 km²). The Salt River, along with the Black River, forms the boundary between the Fort Apache Indian Reservation to the north and the San Carlos Apache Indian Reservation to the south.

The Salt River is fed by numerous perennial streams that start as springs and seeps along the Mogollon Rim and in the White Mountains. The Salt River is perennial from its tributary headwaters to Granite Reef Diversion Dam near Mesa.

From the Black and White confluence, the Salt River flows generally west and southwest. It is joined by Carrizo Creek, a 25-mile (40 km) perennial stream, and then flows through the Salt River Canyon. Cibecue Creek, a 36-mile (58 km) perennial stream, joins the river in the canyon, flowing from the north through the Fort Apache Reservation. Between Carrizo and Cibecue creeks, the Salt River becomes the boundary between the Tonto National Forest on the south and the Fort Apache Reservation on the north. Another perennial stream joins from the north, 46-mile (74 km) long Canyon Creek, followed by Cherry Creek. Just downstream from the Salt's confluence with Medicine Creek, a portion of the Tonto National Forest is designated the Salt River Canyon Wilderness. The Salt River forms the northern and western boundary of the wilderness for several miles, after which the national forest and wilderness occupy both sides of the river.

Continuing its westward course, the Salt River is joined by Pinal Creek from the south, just before leaving the Salt River Canyon Wilderness. The river continues to flow through the Tonto National Forest until leaving the mountains near Mesa. Below the Pinal Creek confluence, the Salt River enters Theodore Roosevelt Lake, the first of four reservoirs on the river. Tonto Creek joins the Salt River in Theodore Roosevelt Lake. Below Theodore Roosevelt Dam, the Salt River passes through the canyon between the Mazatzal Mountains and the Superstition Mountains and is impounded by Horse Mesa Dam (forming Apache Lake) then Mormon Flat Dam (forming Canyon Lake) then Stewart Mountain Dam (forming Saguaro Lake). These four reservoirs are part of the Salt River Project. The water is used by the Phoenix metropolitan area for municipal, industrial, and agricultural purposes. The storage capacity of the reservoirs is 2,910,200 acre-feet (3.5897×10⁹ m³) for Roosevelt, 245,100 acre-feet (302,300,000 m³) for Apache, 57,900 acre-feet (71,400,000 m³) for Canyon, and 69,800 acre-feet (86,100,000 m³) for Saguaro.

As the Salt River passes through its reservoirs, it flows by the Four Peaks Wilderness, near the Four Peaks. A few miles downstream of Stewart Mountain Dam, the last of the four Salt River Project dams, the Verde River joins the Salt from the north. Fountain Hills is located a few miles to the northwest. The Salt River Pima-Maricopa Indian Community is located near the Verde–Salt confluence. The Tonto National Forest ends a couple miles below the Verde River confluence, and the Salt River enters the eastern edge of the greater Phoenix metropolitan area. Less than 1⁄2 mile (0.80 km) from the national forest boundary, the Granite Reef Diversion Dam diverts all remaining water in the Salt River into the Arizona Canal and Southern Canal, which deliver drinking and irrigation water to much of the Phoenix metropolitan area. The dam and canals are part of the Salt River Project.

Below the diversion dam, the bed of the Salt River is dry, except following rain or upstream runoff. The USGS stream gage at 51st Avenue, Phoenix, records no flow at all on many days—in 2009, for example, there was no flow for most of the year, except during parts of February and March when the river's discharge reached an average of 87 cubic feet per second (2.5 m³/s). The diversion capacity at Granite Reef Diversion Dam is 3,600 cubic feet per second (100 m³/s), with 2,000 cubic feet per second (57 m³/s) for the Arizona Canal, and 1,600 cubic feet per second (45 m³/s) for the Southern Canal.