U.S. Route 129 (US 129) is an auxiliary route of US 29, which it intersects in Athens, Georgia. US 129 currently runs for 582 miles (937 km) from and intersection with US 19/US 27 ALT/US 98 in Chiefland, Florida, to an interchange with I-40 in Knoxville, Tennessee. It passes through the states of Florida, Georgia, North Carolina, and Tennessee. It goes through the cities of Macon, Georgia, Athens, Georgia, Gainesville, Georgia, and Knoxville, Tennessee. Eleven miles of US 129 located on the Tennessee/North Carolina border is known as the The Dragon, a popular motorcycle and sports car destination. This name is apparently derived from the roadway's resemblance to a dragon's back. This segment runs from Tab Cat Creek to Deals Gap and has about 318 curves.

U.S. 129 begins at US 19-Alternate US 27-US 98 in Chiefland, Florida, along hidden SR 47 until it reaches Florida State Road 26 in Trenton. From there, the road is signed along Hidden SR 49. It then moves west, briefly overlapping U.S. Route 27(Hidden SR 20) and heads north again in Branford, before that road intersects Florida State Road 349, which used to double as U.S. Route 129 Alternate. From here it intersects with U.S. Route 90 and Florida State Road 51 in Live Oak, taking SR 51 as the new hidden State Road, then meets Interstate 10 at Exit 283, and later Interstate 75 at Exit 451. During a concurrency with U.S. Route 41 in Jasper, U.S. 129 loses SR 51 as a hidden route then after the concurrency ends runs northwest along SR 100 into Georgia.

U.S. 129 provides the primary route between Middle Georgia and Athens. It approaches Athens from the south where it joins the Ga. 10 Loop, a mostly interstate-grade bypass that rings Athens-Clarke County. Here U.S. 129 turns right, toward the northeast, where it runs concurrently with U.S. 78, 29, and 441 along the bypass. US 129 intersects with U.S. 29 northeast of Athens and continues along the GA 10 Loop westward before exiting at Jefferson Road where it winds northwesterly towards Gainesville as one of several routes to Interstate 85 from Athens.

From the Georgia state line, it travels northeast to Topton, where it goes north to Robbinsville followed by Tennessee, through Deals Gap.

The northern terminus of US Highway 129 is at Knoxville, Tennessee. It runs south from the southwestern border of Knoxville and through Alcoa, Tennessee, as Alcoa Highway, then into Deals Gap. From here, it is also known as The Dragon and continues into North Carolina. In the eleven mile (18 km) stretch that ends just past the Tennessee-North Carolina state line, drivers will encounter 318 curves. These curves make this stretch of highway a well known motorcycle/sports car destination for locals and tourists. On weekends, through Spring to the Fall months, visitors are likely to see numerous riders and drivers here to experience the thrill and scenery.