Douglas Fir or Douglas-fir, Pseudotsuga menziesii, is an evergreen conifer native to the coastal regions of western North America, from central California north through Oregon and Washington to British Columbia, Canada. In California, it is found in the Klamath Mountains and the Cascade Range, the California Coast Ranges as far south as the Santa Lucia Mountains in Monterey County, and the Sierra Nevada as far south as the Huntington Lake region in Fresno County.

In California the Douglas Fir and its variety named Coast Douglas Fir (Pseudotsuga menziesii var. menziesii) occur from near sea level along the coast to 5,900 feet (1800 m) in the Sierra Nevada. Eastward they are replaced by its variety named Rocky Mountain Douglas Fir (Pseudotsuga menziesii var. glauca). Its variety named Mexican Douglas Fir (Pseudotsuga menziesii var. lindleyana) is endemic to central and northern montane Mexico.

Douglas Firs commonly live more than 500 years and occasionally more than 1,000 years. The species name, menziesii, honors Archibald Menzies, the first European botanist to document it (1791). The common name honors botanist David Douglas, who introduced it into cultivation (1827). Douglas Firs are commercially important for lumber.

Due to their robust mature size Douglas Fir trees are not frequently planted in small to mid-size residential gardens. Since they can get exceptionally large they need to be provided with plenty of space to grow above and below ground.
Douglas Firs are the second-tallest conifer species in the world after Coast Redwoods (Sequoia sempervirens). Trees 200-250 feet (60-75 meters) in height and trunks 5-6.6 feet (1.5-2 m) in diameter are common in old growth forests. Maximum heights of 330-390 feet (100-120 m) and trunk diameters of 15-20 feet (4.5-6 m) were historically documented. The "Doerner Fir" in Oregon is the tallest known currently living Douglas Fir at 326 ft. (99.4 m) tall; and the "Queets Fir" in Olympic National Park has the widest known currently living trunk at 16 ft. (4.85 m) in diameter.