Port wine (also known as Vinho do Porto, Porto, and often simply port) is a Portuguese fortified wine produced exclusively in the Douro Valley in the northern provinces of Portugal. It is typically a sweet, red wine, often served as a dessert wine, and comes in dry, semi-dry, and white varieties. Fortified wines in the style of port are also produced outside Portugal, most notably in Australia, South Africa, Canada, India, Argentina, and the United States. Under European Union Protected Designation of Origin guidelines, only the product from Portugal may be labelled as port or Porto. In the United States, wines labelled "port" may come from anywhere in the world, while the names "Dão", "Oporto", "Porto", and "Vinho do Porto" have been recognized as foreign, non-generic names for wines originating in Portugal.

Port is produced from grapes grown and processed in the demarcated Douro region. The wine produced is then fortified by the addition of a neutral grape spirit known as aguardente in order to stop the fermentation, leaving residual sugar in the wine, and to boost the alcohol content. The fortification spirit is sometimes referred to as brandy but it bears little resemblance to commercial brandies. The wine is then stored and aged, often in barrels stored in a cave (pronounced KAH-vee and meaning "cellar" in Portuguese) as is the case in Vila Nova de Gaia, before being bottled. The wine received its name, "port", in the latter half of the 17th century from the seaport city of Porto at the mouth of the Douro River, where much of the product was brought to market or for export to other countries in Europe. The Douro valley where port wine is produced was defined and established as a protected region, or appellation in 1756, making it the oldest defined and protected wine region in the world. Chianti (1716) and Tokaj (1730) have older demarcation but no regulation associated and thus, in terms of regulated demarcated regions, Porto is the oldest.

A port is a location on a coast or shore containing one or more harbors where ships can dock and transfer people or cargo to or from land. Port locations are selected to optimize access to land and navigable water, for commercial demand, and for shelter from wind and waves. Ports with deeper water are rarer, but can handle larger, more economical ships. Since ports throughout history handled every kind of traffic, support and storage facilities vary widely, may extend for miles, and dominate the local economy. Some ports have an important military role.

Ports often have cargo-handling equipment, such as cranes (operated by longshoremen) and forklifts for use in loading ships, which may be provided by private interests or public bodies. Often, canneries or other processing facilities will be located nearby. Some ports feature canals, which allow ships further movement inland. Access to intermodal transportation, such as trains and trucks, are critical to a port, so that passengers and cargo can also move further inland beyond the port area. Ports with international traffic have customs facilities. Harbour pilots and tugboats may maneuver large ships in tight quarters when near docks.

Wine is an alcoholic beverage made from fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients.Yeast consumes the sugars in the grapes and converts them into alcohol. Different varieties of grapes and strains of yeasts produce different types of wine.

Wines made from other fruits are usually named after the fruit from which they are produced (for example, apple wine or elderberry wine) and are generically called fruit wine. The term "wine" can also refer to the higher alcohol content of starch-fermented or fortified beverages such as barley wine, sake, and ginger wine.

Wine has a rich history dating back thousands of years, with the earliest known production occurring around 8,000 years ago on the territory of modern-day Georgia. It first appeared in the Balkans about 4500 BC and was very common in ancient Greece, Thrace and Rome. Wine has also played an important role in religion throughout history. The Greek god Dionysus and the Roman equivalent Bacchus represented wine, and the drink is also used in Christian Eucharist ceremonies and the Jewish Kiddush.