Styria (/ˈstɪəriə/; Slovene: Štajerska [ˈʃtáːjɛɾska]), also known as Slovenian Styria (Slovenska Štajerska; Austrian German: Slowenische Steiermark) or Lower Styria (Spodnja Štajerska; Untersteiermark) to differentiate it from Austrian Styria, is a traditional region in northeastern Slovenia, comprising the southern third of the former Duchy of Styria. The population of Styria in its historical boundaries amounts to around 705,000 inhabitants, or 34.5% of the population of Slovenia. Its largest city and urban center is Maribor, with other urban centers including Celje, Velenje, Ptuj and Trbovlje.

In the 19th century, the Styrian duchy, which existed as a distinct political-administrative entity from 1056 to 1918, used to be divided into three traditional regions: Upper Styria (Obersteiermark; Zgornja Štajerska), Central Styria (Mittelsteiermark; Srednja Štajerska), and Lower Styria, stretching from the Mur River and the Slovene Hills in the north down to the Sava. Upper Styria and Central Styria, predominantly German-speaking, today form the Austrian state of Styria (Steiermark). The southern third, predominantly Slovene-speaking Lower Styria, became part of the Kingdom of Serbs, Croats and Slovenes (Yugoslavia) after World War I. After World War II, it became part of the predecessor of modern Slovenia, the Socialist Republic of Slovenia.

Although used interchangeably at times, the term "Southern Styria" (Südsteiermark) refers to the southern districts of the Austrian state of Styria, whereas the term "Lower Styria" (Spodnja Štajerska) refers to the region of Styria in northeastern Slovenia.^{[citation needed]}

The Slovene name Štajerska is borrowed and adapted from the German name for the region, Steiermark. Both ultimately derive from Celtic, via the river Steyr.

In the Middle Ages, the Lower Styrian lands were ruled by several immediate (reichsfrei) dynasties like the Counts of Celje, whose large possessions were not incorporated by the Habsburg dukes until the 15th century.

According to the last Austro-Hungarian census of 1910, Lower Styria had around 498,000 inhabitants, of which around 82% were Slovene and around 18% German speakers.

In 1918, after the disintegration of the Austro-Hungarian monarchy following World War I, the Duchy of Styria was divided between the newly established states of German Austria and the Yugoslav State of Slovenes, Croats and Serbs. In early November 1918, Rudolf Maister, a Slovene major of the former Austro-Hungarian Army, with about 4,000 local volunteers occupied Lower Styria and the town of Maribor and claimed it for Yugoslavia. After a short fight with German-Austrian paramilitary units, the current border was established, acknowledged by the provisional Styrian assembly at Graz. By December 1918, all of Lower Styria was de facto included in the Kingdom of Serbs, Croats, and Slovenes. A protest by German-speaking Marburg citizens resulted in the Marburg Bloody Sunday, when 13 people were killed and about 60 wounded.

Confirmed by the 1919 Treaty of Saint-Germain-en-Laye, the border between Yugoslav and Austrian Styria mostly followed the ethnic-linguistic dividing line between Slovenes and ethnic Germans. Nevertheless, several predominantly German-speaking towns were annexed into Yugoslavia, such as Maribor (Marburg an der Drau) (80% German speakers), Ptuj (Pettau) (86%), and Celje (Cilli) (67%); in addition, the German-speaking area around the village of Apače (Abstall) was annexed to Yugoslavia. According to the 1921 Yugoslav census, some 22,500 ethnic Germans lived in Yugoslav Lower Styria. They represented around 4.5% of the overall population of the region, and around 57% of all ethnic Germans in Slovenia. In 1931, this number dropped to around 12,500 or 2.3% of the regional population, and around 45% of all ethnic Germans in Slovenia.