The Serbian Empire (Serbian: Српско царство / Srpsko carstvo, pronounced [sr̩̂pskoː tsâːrstʋo]) was a medieval Serbian state that emerged from the Kingdom of Serbia. It was established in 1346 by Dušan the Mighty, who significantly expanded the state.

During Dušan's rule, Serbia was one of the most powerful European states and the most powerful in Southeast Europe. It was an Eastern Orthodox multi-ethnic and multi-lingual empire that stretched from the Danube in the north to the Gulf of Corinth in the south, with its capital in Skopje. Dušan also promoted the Serbian Archbishopric to the Serbian Patriarchate. In the Serbian Empire, the region of Kosovo was the most prosperous and densely populated area, serving as a key political, religious, and cultural center.

Dušan's son and successor, Uroš the Weak, struggled to maintain his father's vast empire, gradually losing much of the conquered territory - hence his epithet. The Serbian Empire effectively ended with the death of Uroš V in 1371 and the break-up of the Serbian state. Some successors of Stefan V claimed the title of Emperor in parts of Serbia until 1402, but the territory in Greece was never recovered. From the ruins of the Serbian Empire, Moravian Serbia emerged as the largest and most powerful Serbian state under the rule of the Lazarević dynasty, later playing the key role in the Battle of Kosovo in 1389 against the Ottoman Empire.

Stefan Dušan was the son of the Serbian king Stefan Dečanski (r. 1322–1331). After his father's accession to the throne, Dušan was awarded with the title of "young king". Although this title bore significant power in medieval Serbia, Stefan wanted his younger son, Simeon Uroš, to inherit him instead of Dušan. However, Dušan had significant support from the major part of the Serbian nobility, including the Serbian archbishop Danilo, and some of the king's most trusted generals, such as Jovan Oliver Grčinić. Tensions slowly rose between the king and his son, especially after the battle of Velbužd, where Dušan showed his military capabilities, and they seem to have culminated when king Stefan raided Zeta, a province in Serbia where Dušan ruled autonomously, being a tradition of Serbian heirs to rule this province. Advised by the nobility, Dušan later marched from Zeta to Nerodimlje, where he besieged his father and forced him to surrender the throne. Stefan was later imprisoned in the fortress of Zvečan, where he died.

In 1333, Dušan launched a large attack on the Byzantine empire, at the time ruled by the ambitious emperor Andronikos III Palaiologos, with the help of a deserted Byzantine general, Syrgian. Dušan quickly conquered the cities of Ohrid, Prilep and Kastoria, and attempted to besiege Thessalonica in 1334, but was prevented conquering the city by the death of Syrgian, who had been assassinated by a Byzantine spy. Syrgian was a key figure in Dušan's army, as he had earned a great reputation in Greece, convincing Greek citizens to surrender cities rather than fight Dušan's armies.

By 1345, Dušan the Mighty had expanded his state to cover half of the Balkans, more territory than either the Byzantine Empire or the Second Bulgarian Empire in that time. Therefore, in 1345, in Serres, Dušan proclaimed himself "Tsar" ("Caesar"). On 16 April 1346, in Skopje (former Bulgarian capital), he had himself crowned "Emperor of the Serbs and Greeks", a title signifying a claim to succession of the Byzantine Empire. The ceremony was performed by the newly elevated Serbian Patriarch Joanikije II, the Bulgarian Patriarch Simeon, and Nicholas, the Archbishop of Ohrid. At the same time, Dušan had his son Uroš crowned as King of Serbs and Greeks, giving him nominal rule over the Serbian lands, although Dušan was governing the whole state, with special responsibility for the newly acquired Roman (Byzantine) lands. These actions, which the Byzantines received with indignation, appear to have been supported by the Bulgarian Empire and tsar Ivan Alexander, as the Patriarch of Bulgaria Simeon had participated in both the creation of a Serbian Patriarchate of Peć and the imperial coronation of Stefan Uroš IV Dušan. Dushan made marriage alliance with Bulgarian tsar Ivan Alexander, marrying his sister Helena.

Tsar Dušan doubled the size of Serbian state, seizing territories in all directions, especially south and southeast. Serbia held parts of modern Bosnia and Herzegovina, Moravian Serbia, Kosovo, Zeta, modern North Macedonia, modern Albania, and half of modern Greece. He did not fight a single field battle, instead winning his empire by besieging cities. Dušan undertook a campaign against the Byzantine Empire, which was attempting to avert a deteriorating situation after the destruction caused by the Fourth Crusade. Dušan swiftly seized Thessaly, Albania, Epirus, and most of Macedonia.

After besieging the emperor at Salonica in 1340, he imposed a treaty assuring Serbia sovereignty over regions extending from the Danube to the Gulf of Corinth, from the Adriatic Sea to the Maritsa river, and including parts of southern Bulgaria up to the environs of Adrianople. Bulgaria had never fully recovered since its defeat by the Serbs at the Battle of Velbazhd. The outcome of the battle shaped the balance of power in the Balkans for the next decades to come and although Bulgaria did not lose territory, the Serbs could occupy much of Macedonia. Bulgarian tsar Ivan Alexander, whose sister Helena Dušan later married, became his ally between 1332 and 1365. Dušan ruled over major central part of the Balkan peninsula. He gave sanctuary to the former regent of the Byzantine Empire, John VI Kantakouzenos, in revolt against the government, and agreed to an alliance.