Slavonia (; Croatian: Slavonija) is, with Dalmatia, Croatia proper, and Istria, one of the four historical regions of Croatia. Taking up the east of the country, it roughly corresponds with five Croatian counties: Brod-Posavina, Osijek-Baranja, Požega-Slavonia, Virovitica-Podravina, and Vukovar-Syrmia, although the territory of the counties includes Baranya, and the definition of the western extent of Slavonia as a region varies. The counties cover 12,556 square kilometres (4,848 square miles) or 22.2% of Croatia, inhabited by 806,192—18.8% of Croatia's population. The largest city in the region is Osijek, followed by Slavonski Brod and Vinkovci.
Slavonia is located in the Pannonian Basin, largely bordered by the Danube, Drava, and Sava rivers. In the west, the region consists of the Sava and Drava valleys and the mountains surrounding the Požega Valley, and plains in the east. Slavonia enjoys a moderate continental climate with relatively low precipitation.
After the fall of the Western Roman Empire, which ruled the area of modern-day Slavonia until the 5th century, Ostrogoths and Lombards controlled the area before the arrival of Avars and Slavs, when the Principality of Lower Pannonia was established in the 7th century. It was later incorporated into the Kingdom of Croatia; after its decline, the kingdom was ruled through a personal union with Hungary.
It became part of the Lands of the Hungarian Crown in the 12th century. The Ottoman conquest of Slavonia took place between 1536 and 1552. In 1699, after the Great Turkish War of 1683–1699, the Treaty of Karlowitz transferred Slavonia to the Habsburgs. After the Austro-Hungarian Compromise of 1867, Slavonia became part of the Hungarian part of the realm, and a year later it became part of the Kingdom of Croatia-Slavonia. In 1918, when Austria-Hungary dissolved, Slavonia became a part of the short-lived State of Slovenes, Croats and Serbs which in turn became a part of the Kingdom of Serbs, Croats, and Slovenes, later renamed Yugoslavia. During the Croatian War of Independence of 1991–1995, Slavonia saw fierce fighting, including the 1991 Battle of Vukovar.
The economy of Slavonia is largely based on processing industry, trade, transport, and civil engineering. Agriculture is a significant component of its economy: Slavonia contains 45% of Croatia's agricultural land and accounts for a significant proportion of Croatia's livestock farming and production of permanent crops. The gross domestic product (GDP) of the five counties of Slavonia is worth 6,454 million euro or 8,005 euro per capita, 27.5% below national average. The GDP of the five counties represents 13.6% of Croatia's GDP.
The cultural heritage of Slavonia represents a blend of historical influences, especially those from the end of the 17th century, when Slavonia started recovering from the Ottoman wars, and its traditional culture. Slavonia contributed to the culture of Croatia through art, writers, poets, sculptors, and art patronage. In traditional music, Slavonia comprises a distinct region of Croatia, and the traditional culture is preserved through folklore festivals, with prominence given to tamburica music and bećarac, a form of traditional song, recognized as an intangible cultural heritage by UNESCO. The cuisine of Slavonia reflects diverse influences—a blend of traditional and foreign elements. Slavonia is one of Croatia's winemaking areas, with Ilok and Kutjevo recognized as centres of wine production.