State Route 299 is a state highway in the U.S. state of California that runs across the northern part of the state. The highway begins at US 101 at the northern edge of Arcata, 9 miles north of Eureka on the Pacific and continues in an easterly direction through to the Nevada stateline. Between Arcata and Redding, Route 299 junctions with State Route 96 and is briefly co-signed with State Route 3. In Redding, it intersects with State Route 273 and State Route 44 and Interstate 5. East of Redding, it intersects with State Route 89 and a section is co-signed with State Route 139 before reaching Alturas. It is then co-signed with U.S. Route 395 north-east of Alturas, then it runs east towards the border with Nevada. A ghost town, Vya, Nevada, can be reached via this route, which after the border becomes a dirt road, which was formerly Nevada State Route 8A.

Part of SR 299 is the Trinity Scenic Byway, a Forest Service Byway.

SR 299 is part of the California Freeway and Expressway System and is eligible for the State Scenic Highway System.

SR 299 begins in Arcata at a trumpet interchange with US 101 as a freeway. The route has another trumpet interchange with SR 200 after leaving the Arcata city limits and crossing the Mad River. The freeway ends in the city of Blue Lake as SR 299 continues east past the truck scales. SR 299 enters Six Rivers National Forest and intersects SR 96 at Willow Creek. Soon after this, SR 299 crosses into Trinity County and Trinity National Forest. Paralleling the Trinity River, SR 299 passes through Salyer (where there is a rest area), Hawkins Bar, California, Burnt Ranch, Del Loma, Big Bar, Helena, Junction City, and finally Weaverville.

In Weaverville, SR 299 runs concurrently with SR 3 southbound to Douglas City, where there is a rest area. SR 299 continues east away from the Trinity River into Shasta County, passing by the Whiskeytown-Shasta National Recreation Area and through the towns of Tower House and Whiskeytown as well as Whiskeytown Lake. SR 299 continues along Eureka Way through the town of Shasta into the city of Redding. SR 299 runs concurrently along SR 273 north across the Sacramento River before turning east onto its own freeway and intersecting I-5.[citation needed] SR 299 remains a freeway for a few miles before leaving the Redding city limits and passing through the town of Bella Vista.

SR 299 continues through Ingot, Round Mountain, Montgomery Creek, Hillcrest (after the rest area), Burney, and Johnson Park. The highway intersects with SR 89 before continuing through Fall River Mills and McArthur, where there is an intersection with CR A19. SR 299 then crosses into Lassen County, where it passes through Nubieber and Bieber before intersecting CR A2. The highway crosses into Modoc County and passes through Adin, where it runs concurrently with SR 139 and passes through Modoc National Forest. The concurrency lasts for several miles before SR 299 turns east and enters the city of Alturas. SR 299 runs concurrently with US 395 before turning east again and passing through Cedarville, near the Cedarville Airport. SR 299 ends at the Nevada state line.

State Route 299, from the intersection with US 101 all the way to US 395 in Alturas, was U.S. Route 299 from 1934 to 1964, but the actual road has been realigned many times, mainly to make easier grades and curves through the mountains. In many places, especially in Trinity County, the old concrete can be seen beside the new road, and there is even an arch bridge from 1923 visible from the current 299, that seemingly connects nothing to nothing nowadays. In 1934, it was the original California State Route 44.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.