Great Moravia, or simply Moravia, was the first major state that was predominantly West Slavic to emerge in the area of Central Europe, possibly including territories which are today part of the Czech Republic, Slovakia, Hungary, Austria, Germany, Poland, Romania, Croatia, Serbia, Ukraine and Slovenia. The formations preceding it in these territories were Samo's tribal union (631–658) and the Pannonian Avar state (567–822).

Centered on the Morava River – which gave the realm its name – the core encompassed today’s Moravia in the eastern Czech Republic and adjacent western Slovakia. The kingdom saw the rise of the first-ever Slavic literary culture in the Old Church Slavonic language as well as the expansion of Christianity, first via missionaries from East Francia, and later after the arrival of Saints Cyril and Methodius in 863 and the creation of the Glagolitic alphabet, the first alphabet dedicated to a Slavic language. Glagolitic was subsequently replaced by the Cyrillic alphabet created in the First Bulgarian Empire.

Although the borders of this empire cannot be exactly determined, Moravia reached its largest territorial extent under Prince Svatopluk I (Slovak: Svätopluk), who ruled from 870 to 894. Separatism and internal conflicts emerging after Svatopluk's death contributed to the fall of Great Moravia, which was overrun by the Hungarians, who then included the territory of present-day Slovakia in their domains. The exact date of Moravia's collapse is unknown, but it occurred between 902 and 907.

Moravia experienced significant cultural development under King Rastislav, with the arrival in 863 of the mission of Saints Cyril and Methodius. After his request for missionaries had been refused in Rome, Rastislav asked the Byzantine emperor to send a "teacher" (učiteľ) to introduce literacy and a legal system (pravьda) to Great Moravia. The request was granted. The missionary brothers Cyril and Methodius introduced a system of writing (the Glagolitic alphabet) and Slavonic liturgy, the latter eventually formally approved by Pope Adrian II. The Glagolitic script was probably invented by Cyril himself and the language he used for his translations of religious texts and his original literary creation was based on the Eastern South Slavic dialect he and his brother Methodius knew from their native Thessaloniki. Old Church Slavonic, therefore, differed somewhat from the local Slavic dialect of Great Moravia which was the ancestral idiom to the later dialects spoken in Moravia and western Slovakia. Later, the disciples of Cyril and Methodius were expelled from Great Moravia by King Svatopluk I, who re-orientated the Empire to Western Christianity.

The meaning of the name of Great Moravia has been subject to debate. The designation "Great Moravia"—Megale Moravia (Μεγάλη Μοραβία) in Greek—stems from the work De Administrando Imperio written by the Byzantine Emperor Constantine VII Porphyrogenitos around 950. The emperor only used the adjective megale in connection with the polity when referring to events that occurred after its fall, implying that it should rather be translated as "old" instead of "great". According to a third theory, the megale adjective refers to a territory located beyond the borders of the Byzantine Empire. Finally, the historian Lubomír E. Havlík writes that Byzantine scholars used this adjective when referring to homelands of nomadic peoples, as demonstrated by the term "Great Bulgaria".

[There] is Belgrade, in which is the tower of the holy and great Constantine, the emperor; then, again, at the running back of the river, is the renowned Sirmium by name, a journey of two days from Belgrade; and beyond lies great Moravia, the unbaptized, which the [Hungarians] have blotted out, but over which in former days [Svatopluk] used to rule. Such are the landmarks and names along the Danube river [...].

— Constantine Porphyrogenitus: De Administrando Imperio

The work of Porphyrogenitos is the only nearly contemporaneous source using the adjective "great" in connection with Moravia. Other documents from the 9th and 10th centuries never used the term in this context. Instead they mention the polity as "Moravian realm" or "realm of Moravians" (regnum Marahensium, terra Marahensium, regnum Marahavorum, regnum Marauorum, terra Marauorum or regnum Margorum in Latin, and Moravьska oblastь in Old Church Slavonic), simply "Moravia" (Marawa, Marauia, and Maraha in Latin, Morava, Marava, or Murava in Old Church Slavonic, and M.ŕawa.t in Arabic), also regnum Sclavorum (realm of Slavs) or alternate regnum Rastizi (realm of Rastislav) or regnum Zuentibaldi (realm of Svatopluk).