The Douro region of northern Portugal is the home of Port. It takes its name from the Douro river, which flows east to west from the Spanish border to Oporto, where it meets the Atlantic Ocean. Though Douro is best known for its fortified wines, total production here is fairly evenly split between Port and non-fortified table wines.

The viticultural zone covers the steep slopes along the banks of the lower reaches of the river, which is one of the longest on the Iberian peninsula. From its source in northern Spain, where it is known as the Duero, it flows through the famous vineyards of Ribera del Duero before finding the Portuguese border and becoming the Douro. From here, it cuts through the landscape, creating a unique and historic wine region before meeting the ocean at Oporto.

The Douro's most unifying trait is its mountainous terrain, although the area covers a broad array of terroir with any number of different aspects, altitudes and soil types. Typically, however, the vineyards stretch up the steep, dry slopes on either side of the river and its myriad tributaries on narrow rocky terraces – a sight that has been classified as a Unesco World Heritage site.

There are three recognized subregions of the Douro, each covering a section of the river as it flows toward Oporto. These subregions each express different aspects of the area's hot continental climate. The Douro Superior region is the furthest inland, sharing its border with that of Portugal itself. This emerging subregion is covered in terraced vineyards and takes up about 20 percent of available vineyard land in Douro.

The central part of the Douro region, centred on the village of Pinhão, is known as the Cima Corgo region, where most high-end Vintage Port originates. Cima Corgo is the largest of the Douro's three subregions, and accounts for almost half of the valley's total wine production. The steep vineyards of Cima Corgo are predominantly composed of schist with sizable granite deposits. Vines nearer the river tend to ripen much earlier than those at higher elevations, as the river holds warmth more readily than the air. This discrepancy in the climate means that the harvest is often completed in multiple sweeps of the same vineyard.

Nearest Oporto and the coast is the Baixo Corgo (Lower Corgo) subregion, the area best suited to the production of table wines. The area is cooler and wetter than its neighbours, but also more accessible, meaning that more bulk-wine operations are possible.

Fortified wines have been made on the steep banks of the Douro since the 17th Century, although vines have grown there for much longer.

The history of still wines in the Douro has been plagued by poor quality until only recently, starting with the "blackstrap" wines that were popular before Port took off in the 1700s. In 1979, the Douro's official demarcation was extended to include still wines along with fortified wines, and in the 1990s, production increased considerably. Today, Douro makes some of Portugal's most prestigious red table wines from the area's array of indigenous grape varieties.

The Douro's wines – both still and fortified – can be made from more than 80 different grape varieties, but in practice the vineyards are dominated by five key varieties: Touriga Nacional, Touriga Franca, Tinta Barroca, Tinto Cao and Tinta Roriz (Tempranillo). Of these, aromatic Touriga Nacional is the most highly regarded, and Touriga Franca the most widely planted. Vineyards tend to be an eclectic cross-section of port grape varieties, often with more than 20 present within a single vineyard. Often, the winemaker will not even be sure of the exact proportion of each variety in a given wine.

A number of international varieties have also found a home in the Douro valley, particularly for the production of table wines. Cabernet Sauvignon, Sauvignon Blanc and Gewürztraminer are among the more common non-native grapes planted here.