The springs at Baden-Baden were known to the Romans as Aquae ("The Waters") and Aurelia Aquensis ("Aurelia-of-the-Waters") after M. Aurelius Severus Alexander Augustus.
In modern German, Baden is a noun meaning "bathing" but Baden, the original name of the town, derives from an earlier plural form of Bad ("bath"). (The modern plural has become Bäder.) As with the English placename "Bath", there are various other Badens at hot springs throughout Central Europe. The current doubled name arose to distinguish it from the others, particularly Baden near Vienna in Austria and Baden near Zürich in Switzerland. It is a reference to the Margraviate of Baden-Baden (1535–1771), a subdivision of the Margraviate of Baden, the territory named after the town. Baden-Baden got its formal name in 1931.
Baden-Baden lies in a valley of the Northern Black Forest in southwestern Germany. The western districts lie within the Upper Rhine Plain. The highest mountain of Baden-Baden is the Badener Höhe (1,002.5 m above sea level (NHN)), which is part of the Black Forest National Park. The old town lies on the side of a hill on the right bank of the Oos. Since the 19th century, the principal resorts have been located on the other side of the river. There are 29 natural springs in the area, varying in temperature from 46 to 67 °C (115 to 153 °F). The water is rich in salt and flows from artesian wells 1,800 m (5,900 ft) under Florentine Hill at a rate of 341 litre (90 gallons) per minute and is conveyed through pipes to the town's baths.
Roman settlement at Baden-Baden has been dated as far back as the emperor Hadrian, but on dubious authority. The known ruins of the Roman bath were rediscovered just below the New Castle in 1847 and date to the reign of Caracalla (AD 210s), who visited the area to relieve his arthritic aches. The facilities were used by the Roman garrison in Strasbourg.
The town fell into ruin but its church was first constructed in the 7th century. By 1112, it was the seat of the Margraviate of Baden. The Lichtenthal Convent (Kloster Lichtenthal) was founded in 1254. The margraves initially used Hohenbaden Castle (the Old Castle, Altes Schloss), whose ruins still occupy the summit above the town, but they completed and moved to the New Castle (Neues Schloss) in 1479. Baden suffered severely during the Thirty Years' War, particularly at the hands of the French, who plundered it in 1643. They returned to occupy the city in 1688 at the onset of the Nine Years' War, burning it to the ground the next year. The margravine Sibylla rebuilt the New Castle in 1697, but the margrave Louis William removed his seat to Rastatt in 1706. The Stiftskirche was rebuilt in 1753 and houses the tombs of several of the margraves.
The town began its recovery in the late 18th century, serving as a refuge for émigrés from the French Revolution. The town was frequented during the Second Congress of Rastatt in 1797–99 and became popular after the visit of the Prussian queen in the early 19th century. She came for medicinal reasons, as the waters were recommended for gout, rheumatism, paralysis, neuralgia, skin disorders, and stones. The Ducal government subsequently subsidized the resort's development. The town became a meeting place for celebrities, who visited the hot springs and the town's other amenities: luxury hotels, the Spielbank Casino, horse races, and the gardens of the Lichtentaler Allee. Guests included Queen Victoria, Wilhelm I, and Berlioz. The pumproom (Trinkhalle) was completed in 1842. The Grand Duchy's railway's mainline reached Baden in 1845. Reaching its zenith under Napoleon III in the 1850s and '60s, Baden became "Europe's summer capital". With a population of around 10 000, the town's size could quadruple during the tourist season, with the French, British, Russians, and Americans all well represented. (French tourism fell off following the Franco-Prussian War.)
The theater was completed in 1861 and a Greek church with a gilt dome was erected on the Michaelsberg in 1863 to serve as the tomb of the teenage son of the prince of Moldavia Mihail Sturdza after he died during a family vacation. A Russian Orthodox church was also subsequently erected. The casino was closed for a time in the 1870s.
Just before the First World War, the town was receiving 70 000 visitors each year. The town escaped destruction through both world wars. After World War II, Baden-Baden became the headquarters of the French occupation forces in Germany as well as of the Südwestfunk, one of Germany's large public broadcasting stations, which is now part of Südwestrundfunk. From 23–28 September 1981, the XIth Olympic Congress took place in Baden-Baden's Kurhaus. The Festspielhaus Baden-Baden, Germany's largest opera and concert house, opened in 1998.
CFB Baden-Soellingen, a military airfield built in the 1950s in the Upper Rhine Plain, 10 km (6 mi) west of downtown Baden-Baden, was converted into a civil airport in the 1990s. Karlsruhe/Baden-Baden Airport, or Baden Airpark is now the second-largest airport in Baden-Württemberg by number of passengers.
Baden-Baden is a German spa town. The city offers many options for sports enthusiasts; golf and tennis are both popular in the area. Horse races take place each May, August and October at nearby Iffezheim. The countryside is ideal for hiking and mountain climbing. In the winter Baden-Baden is a skiing destination. There is an 18-hole golf course in Fremersberg.
Climate in this area has mild differences between highs and lows, and there is adequate precipitation year round. The Köppen Climate Classification subtype for this climate is "Cfb" (Marine West Coast Climate/Oceanic climate).
Baden featured in Tolstoy's Anna Karenina (under an alias) and Turgenev's Smoke. Dostoyevsky wrote The Gambler while compulsively gambling at the town's casino.
The 1975 film The Romantic Englishwoman was filmed on location in Baden-Baden, featuring the Brenner's Park Hotel particularly prominently. The 1997 Bollywood movie Dil To Pagal Hai was also shot in the town.