The Willamette Valley (/wᵻˈlæmᵻt/) is a 150-mile (240 km) long valley in the Pacific Northwest region of the United States, located entirely within the state of Oregon. The valley forms the cultural and political heart of Oregon and is home to approximately 70 percent of its population including Portland, its largest city, as well as Salem, the state capital. The Willamette River flows the entire length of the valley, which is surrounded by mountains on three sides - the Oregon Coast Range to the west, the Cascade Range to the east, and the Calapooya Mountains to the south.

The valley's numerous waterways, particularly the Willamette River, remain vitally important to the economy of Oregon, as they continuously deposit highly fertile alluvial soils across its broad, flat plain. A massively productive agricultural area, the valley was widely publicized in the 1820s as a 'promised land of flowing milk and honey'. Throughout the 19th century it was the destination of choice for the oxen-drawn wagon trains of emigrants who made the perilous journey along the Oregon Trail.

The Willamette Valley AVA (/wᵻˈlæmᵻt/ wi-LAM-it), is an American Viticultural Area which lies in the Willamette Valley of Oregon. The AVA is the wine growing region which encompasses the drainage basin of the Willamette River. It stretches from the Columbia River in the north to just south of Eugene in the south, where the Willamette Valley ends; and from the Oregon Coast Range in the west to the Cascade Mountains in the east. At 5,200 square miles (13,500 km²), it is the largest AVA in the state, and contains most of the state's wineries; approximately 200 as of 2006. The boundaries of the Willamette Valley AVA were established in 1984, and since then six new, smaller AVAs have been created within the northern portion of Willamette Valley AVA. The Willamette Valley has a cool, moist climate, and is recognized worldwide for its Pinot noir.

Although this distinction is not officially recognized, many wine connoisseurs further divide the Willamette Valley into northern and southern regions, the dividing line being the approximate latitude of Salem (approximately 45° north latitude).

The Willamette Valley is a geographic region in northwest Oregon, United States.

Willamette Valley may also refer to:

The Willamette Valley ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency in the U.S. states of Oregon and Washington. Slightly larger than the Willamette Valley for which it is named, the ecoregion contains fluvial terraces and floodplains of the Willamette River system, scattered hills, buttes, and adjacent foothills. It is distinguished from the neighboring Coast Range, Cascades, and Klamath Mountains ecoregions by lower precipitation, lower elevation, less relief, and a different mosaic of vegetation. Mean annual rainfall is 37 to 60 inches (96 to 152 cm), and summers are generally dry. Historically, the region was covered by rolling prairies, oak savanna, coniferous forests, extensive wetlands, and deciduous riparian forests. Today, it contains the bulk of Oregon’s population, industry, commerce, and agriculture. Productive soils and a temperate climate make it one of the most important agricultural areas in Oregon.

The Willamette Valley, also known as the Willamette Valley Express, was a passenger train operated by Amtrak between Portland, Oregon and Eugene, Oregon. The name came from the Willamette Valley region which the train ran through. Amtrak introduced the train on August 3, 1980 with support from the state of Oregon. The new twice-daily service supplemented the long-distance Coast Starlight and added stops at Milwaukie and Woodburn. The Willamette Valley carried a cafe car and unreserved coaches. The initial trial run was slated to last until June 30, 1981. Two Willamette Valleys (#751 and #753) operated southbound in the morning and afternoon, respectively, while one (#752) operated northbound in the early afternoon. Amtrak began originating the Mount Rainier (#790) in Eugene instead of Portland for the morning northbound service.

In July 1981 the federal government approved funding to continue the trains through 1984 provided that Oregon continued to pay one-third of the subsidy. In early August the state legislature approved additional funds to keep the trains running through the end of 1981 amid concerns over a fare hike and falling ridership. Amtrak discontinued the Willamette Valley at the end of the year after Oregon declined to continue funding the trains. The Willamette Valley made its final run on December 31, 1981.