The Province of Upper Silesia (German: Provinz Oberschlesien; Silesian German: Provinz Oberschläsing; Silesian: Prowincyjŏ Gōrny Ślōnsk; Polish: Prowincja Górny Śląsk) was a province of the Free State of Prussia from 1919 to 1945. It comprised much of the region of Upper Silesia and was eventually divided into two government regions (Regierungsbezirke) called Kattowitz (1939–1945), and Oppeln (1819–1945). The provincial capital was Oppeln (1919–1938) and Kattowitz (1941–1945), while other major towns included Beuthen, Gleiwitz, Hindenburg O.S., Neiße, Ratibor and Auschwitz, added in 1941 (the place of future extermination of Jews in World War II). Between 1938 and 1941 it was reunited with Lower Silesia as the Province of Silesia.

Perhaps the earliest exact census figures on ethnic or national structure of Regierungsbezirk Oppeln (Regierungsbezirk Kattowitz did not yet exist) are from 1819. In 1819 the Oppeln Region had 561,203 inhabitants, including the following "Nationalverschiedenheit":

The population more than doubled during the next five decades, reaching over 1,2 million inhabitants by year 1867, including around 742 thousand Poles and around 457 thousand Germans. The indigenous Polish population was subjected to Germanisation policies. The last pre-World War I general census figures available, are from 1910 (if not including the 1911 census of school children - Sprachzählung unter den Schulkindern - which revealed a higher percent of Polish-speakers among school children than the 1910 census among the general populace). Large demographic changes took place between 1819 and 1910, with the region's total population quadrupling, the percent of German-speakers increasing significantly, and that of Polish-speakers declining considerably. Also the total land area in which Polish was spoken, as well as the land area in which it was spoken by the majority, declined between 1790 and 1890. Polish authors before 1918 estimated the number of ethnic Poles in Prussian Upper Silesia as slightly higher than according to figures from official German censuses.

Exact ethnolinguistic figures for the 19th century and early 20th century can be found in Table 1.:

From 1919 to 1921 three Silesian Uprisings occurred among the Polish-speaking populace of Upper Silesia; the Battle of Annaberg was fought in the region in 1921. In the Upper Silesia plebiscite of March 1921, 59,4% voted against merging with Poland and 40,6% voted for, with clear lines dividing Polish and German communities. The exact border, the maintenance of cross-border railway traffic and other necessary co-operations, as well as equal rights for all inhabitants in both parts of Upper Silesia, were all fixed by the German-Polish Accord on East Silesia, signed in Geneva on 15 May 1922. On 20 June the Weimar Republic ceded, de facto, the eastern parts of Upper Silesia, becoming part of the Silesian Voivodeship of the Second Polish Republic. Within Weimar Germany, the Prussian Province of Silesia was divided into the provinces of Upper Silesia and Lower Silesia The territory remaining in Prussian Upper Silesia was administered within the Oppeln Region and — according to Polish sources — had 530,000 Poles within it.

After the Nazis' takeover in Germany, anti-Semitic laws were also introduced in German Upper Silesia, against the German-Polish Accord on East Silesia of 1922. Among other stipulations, according to the treaty each contractual party guaranteed in its respective part of Upper Silesia equal civil rights for all the inhabitants. The German Upper Silesian Franz Bernheim succeeded in convincing the League of Nations to force Nazi Germany to abide by the Accord, by filing the Bernheim petition. Accordingly, in September 1933 the Reich's Nazi government suspended in German Upper Silesia all anti-Semitic discrimination laws already imposed and excepted the province from all new such future decrees, until the Accord expired in May 1937.

The Polish population was also increasingly persecuted. The first conference of the Nazi anti-Polish organization Bund Deutscher Osten in Upper Silesia was held on 9 June 1933 in Gliwice. A secret Sicherheitsdienst report from 1934, mentioned Bytom, Gliwice, Prudnik, Strzelce Opolskie, Zabrze and the Olesno and Opole rural districts as the main centers of the Polish movement in the province. In August 1937, the Germans arrested 31 Polish youth activists.

The Province of Upper Silesia was joined to Lower Silesia to form the Province of Silesia in 1938. The persecution of Poles then further intensified.