Wuppertal (German pronunciation: [ˈvʊpɐtaːl] ^ⓘ; lit. 'Wupper Dale') is a city in North Rhine-Westphalia, in western Germany, with a population of 355,000. Wuppertal is the seventh-largest city in North Rhine-Westphalia and 17th-largest in Germany. It was founded in 1929 by the merger of Elberfeld, Barmen, Ronsdorf, Cronenberg and Vohwinkel, and was initially called "Barmen-Elberfeld" before adopting its present name in 1930. It is the capital and largest city of the Bergisches Land.

The city straddles the densely populated banks of the River Wupper, a tributary of the Rhine. Wuppertal is located between the Ruhr (Essen) to the north, Düsseldorf to the west, and Cologne to the southwest, and over time has grown together with Solingen, Remscheid and Hagen. The stretching of the city in a long band along the narrow Wupper Valley leads to a spatial impression of Wuppertal being larger than it actually is. The city is known for its steep slopes, its woods and parks, and for being the greenest city in Germany, with two-thirds green space of the total municipal area. From any part of the city, it is only a ten-minute walk to one of the public parks or woodland paths.

The Wupper Valley was, along with the Ore Mountains and before the Ruhr, the first highly industrialized region of Germany, which resulted in the construction of the Wuppertal Schwebebahn suspension railway in the then independent cities of Elberfeld and Barmen. The increasing demand for coal from the textile mills and blacksmith shops from those cities encouraged the expansion of the nearby Ruhr. Wuppertal still is a major industrial centre, being home to industries such as textiles, metallurgy, chemicals, pharmaceuticals, electronics, automobiles, rubber, vehicles and printing equipment. Aspirin originates from Wuppertal, patented in 1897 by Bayer, as does the Vorwerk Kobold vacuum cleaner. The Wuppertal Institute for Climate, Environment and Energy and the European Institute for International Economic Relations are located in the city. Barmen was the birthplace of Friedrich Engels. Due to the city's length, the Bergish varieties of the Limburgish language called Platt are spoken in its western communities like Vohwinkel, but not in the city's eastern communities like Langenfeld where the Southern varieties of Westphalian language are spoken and the city is called Wupperdaal by locals.

Wuppertal in its present borders was formed in 1929 by merging the industrial cities of Barmen and Elberfeld along with the communities of Vohwinkel, Ronsdorf, Cronenberg, Langerfeld and Beyenburg. The initial name Barmen-Elberfeld was changed in a 1930 referendum to Wuppertal ("Wupper Valley"). The new city was administered as part of Prussia's Rhine Province.

Uniquely for Germany, it is a "linear city", owing to the steep hillsides along the river Wupper. Its highest hill is the Lichtscheid, which is 351 m (1,152 ft) above sea level. The dominant urban centres Elberfeld (historic commercial centre) and Barmen (more industrial) have formed a continuous urbanized area since 1850. During the succeeding decades, "Wupper-Town" became the dominant industrial agglomeration of northwestern Germany. During the 20th century, this conurbation had been surpassed by Cologne, Düsseldorf and the Ruhr area, all with a more favourable topography.

From 5 July 1933 to 19 January 1934 the Kemna concentration camp was established in Wuppertal. It was one of the early Nazi concentration camps, created by the Nazi Party to incarcerate their political opponents upon gaining power in 1933. The camp was established in a former factory on the Wupper in the Kemna neighborhood of the Barmen part of Wuppertal. Protestant Christians opposed to the so called German Christians adopted the Barmen Declaration in Wuppertal in 1934.

By order of 10 October 1938, the 1st Light Division of the German Army was formed in Wuppertal, which in September 1939 took part in the invasion of Poland which started World War II. During the war, Nazi Germany operated a Nazi prison, two forced labour subcamps of the prison in Remscheid-Lüttringhausen and an SS construction brigade in the city. The prisoners of the SS construction brigade were Poles, Russians, French, Czechs, Romanians, Hungarians, and Greeks. About 40% of buildings in the city were destroyed by Allied bombing, as were many other German cities and industrial centres (see Bombing of Wuppertal in World War II). However, a large number of historic sites have been preserved, such as:

The US 78th Infantry Division under Major General Edwin P. Parker Jr. captured Wuppertal against scant resistance on 16 April 1945. Wuppertal became a part of the British Zone of Occupation, and subsequently part of the new state of North Rhine-Westphalia in West Germany.