South Slavs are Slavic people who speak South Slavic languages and inhabit a contiguous region of Southeast Europe comprising the eastern Alps and the Balkan Peninsula. Geographically separated from the West Slavs and East Slavs by Austria, Hungary, Romania, and the Black Sea, the South Slavs today include Bosniaks, Bulgarians, Croats, Macedonians, Montenegrins, Serbs and Slovenes.

In the 20th century, the country of Yugoslavia (from Serbo-Croatian, literally meaning "South Slavia" or "South Slavdom") united a majority of the South Slavic peoples and lands—with the exception of Bulgarians and Bulgaria—into a single state. The Pan-Slavic concept of Yugoslavia emerged in late 17th-century Croatia, at the time part of the Habsburg monarchy, and gained prominence through the 19th-century Illyrian movement. The Kingdom of Serbs, Croats and Slovenes, renamed the Kingdom of Yugoslavia in 1929, was proclaimed on 1 December 1918, following the unification of the State of Slovenes, Croats and Serbs with the kingdoms of Serbia and Montenegro. With the breakup of Yugoslavia in the early 1990s, several independent sovereign states were formed.

The term "Yugoslavs" was and sometimes is still used as a synonym for "South Slavs", but it usually excludes Bulgarians since Bulgaria never formed part of the former Yugoslavia.

The South Slavs are known in Serbian, Macedonian, and Montenegrin as Južni Sloveni (Cyrillic: Јужни Словени); in Bulgarian as Yuzhni Slavyani (Cyrillic: Южни славяни); in Croatian and Bosnian as Južni Slaveni (Bosnian: Јужни Славени); and in Slovene as Južni Slovani. The Slavic root *jug- means 'south'. The Slavic ethnonym itself was used by 6th-century writers to describe the southern group of Early Slavs (the Sclaveni); West Slavs were called Veneti and East Slavs Antes. The South Slavs are also called Balkan Slavs.

Another name popular in the early modern period was Illyrians, using the name of a pre-Slavic Balkan people, a name first adopted by Dalmatian intellectuals in the late 15th century to refer to South Slavic lands and population. It was then used by the Habsburg monarchy and France, and notably adopted by the 19th-century Croatian Illyrian movement. Eventually, the idea of Yugoslavism appeared, aimed at uniting all South Slav-populated territories into a common state. From this idea emerged Yugoslavia—which, however, did not include Bulgaria.^{[citation needed]}

The Proto-Slavic homeland is the postulated area of Slavic settlement in Central and Eastern Europe during the first millennium AD, with its precise location debated by archaeologists, ethnographers and historians. None of the proposed homelands reaches the Volga River in the east, over the Dinaric Alps in the southwest or the Balkan Mountains in the south, or past Bohemia in the west. Traditionally, scholars place it in the marshes of Ukraine, or alternatively between the Bug and the Dnieper; however, according to F. Curta, the homeland of the southern Slavs mentioned by 6th-century writers was just north of the Lower Danube. Little is known about the Slavs before the 5th century, when they began to spread out in all directions.^{[citation needed]}

Jordanes (fl.  6th century CE), Procopius (c. 500 - c. 565) and other late Roman authors provide the probable earliest references to southern Slavs in the second half of the 6th century. Procopius described the Sclaveni and Antes as two barbarian peoples with the same institutions and customs since ancient times, not ruled by a single leader but living under democracy, while Pseudo-Maurice called them a numerous people, undisciplined, unorganized and leaderless, who did not allow enslavement and conquest, and resistant to hardship, bearing all weathers. They were portrayed by Procopius as unusually tall and strong, of dark skin and "reddish" hair (neither blond nor black), leading a primitive life and living in scattered huts, often changing their residence. Procopius said they were henotheistic, believing in the god of lightning (Perun), the ruler of all, to whom they sacrificed cattle. They went into battle on foot, charging straight at their enemy, armed with spears and small shields, but they did not wear armour.

While archaeological evidence for a large-scale migration is lacking, most present-day historians claim that Slavs invaded and settled the Balkans in the 6th and 7th centuries. According to this dominant narrative, up until the late 560s their main activity southward across the Danube was raiding, though with limited Slavic settlement mainly through Byzantine colonies of foederati. The Danube and Sava frontier was overwhelmed by large-scale Slavic settlement in the late 6th and early 7th century. What is today central Serbia was an important geo-strategical Byzantine province, through which the Via Militaris crossed. This area was frequently intruded upon by barbarians in the 5th and 6th centuries. From the Danube, the Slavs commenced raiding the Byzantine Empire on an annual basis from the 520s, spreading destruction, taking loot and herds of cattle, seizing prisoners and capturing fortresses. Often, the Byzantine Empire was stretched, defending its rich Asian provinces from Arabs, Persians and others. This meant that even numerically small, disorganised early Slavic raids were capable of causing much disruption, but could not capture the larger, fortified cities. The first Slavic raid south of the Danube was recorded by Procopius, who mentions an attack of the Antes, "who dwell close to the Sclaveni", probably in 518. Sclaveni are first mentioned in the context of the military policy on the Danube frontier of Byzantine Emperor Justinian I (r. 527–565). Throughout the 6th century, Slavs raided and plundered deep into the Balkans, from Dalmatia to Greece and Thrace, and were also at times recruited as Byzantine mercenaries, fighting the Ostrogoths. Justinian seems to have used the strategy of 'divide and conquer', and the Sclaveni and Antes are mentioned as fighting each other. The Antes are last mentioned as anti-Byzantine belligerents in 545, and the Sclaveni continued to raid the Balkans. In 558 the Avars arrived at the Black Sea steppe, and defeated the Antes between the Dnieper and Dniester. The Avars subsequently allied themselves with the Sclaveni, although there was an episode in which the Sclavene Daurentius (fl.  577–579), the first Slavic chieftain recorded by name, dismissed Avar suzerainty and retorted that "Others do not conquer our land, we conquer theirs [...] so it shall always be for us", and had the Avar envoys slain. By the 580s, as the Slav communities on the Danube became larger and more organized, and as the Avars exerted their influence, raids became larger and resulted in permanent settlement. Most scholars consider the period of 581–584 as the beginning of large-scale Slavic settlement in the Balkans. F. Curta points out that evidence of substantial Slavic presence does not appear before the 7th century and remains qualitatively different from the "Slavic culture" found north of the Danube. In the mid-6th century, the Byzantines re-asserted their control of the Danube frontier, thereby reducing the economic value of Slavic raiding. This growing economic isolation, combined with external threats from the Avars and Byzantines, led to political and military mobilisation. Meanwhile, the itinerant form of agriculture (lacking crop rotation) may have encouraged micro-regional mobility. Seventh-century archaeological sites show earlier hamlet-collections evolving into larger communities with differentiated zones for public feasts, craftmanship, etc. It has been suggested that the Sclaveni were the ancestors of the Serbo-Croatian group while the Antes were those of the Bulgarian Slavs, with much mixture in the contact zones. The diminished pre-Slavic inhabitants, also including Romanized native peoples, fled from the barbarian invasions and sought refuge inside fortified cities and islands, whilst others fled to remote mountains and forests and adopted a transhumant lifestyle. The Romance-speakers within the fortified Dalmatian city-states managed to retain their culture and language for a long time. Meanwhile, the numerous Slavs mixed with and assimilated the descendants of the indigenous population.