Grand prince or great prince (feminine: grand princess or great princess) (Latin: magnus princeps; Swedish: storfurste; German: Großfürst; Greek: Μέγας Αρχών, romanized: Megas Archon; Russian: великий князь, romanized: velikiy knyaz) is a hereditary title, used either by certain monarchs or by members of certain monarchs' families.

Grand duke is the usual and established, though not literal, translation of these terms in English and Romance languages, which do not normally use separate words for a "prince" who reigns as a monarch (e.g., Albert II, Prince of Monaco) and a "prince" who does not reign, but belongs to a monarch's family (e.g., Prince George of Wales). Some Slavic (Królewicz), Germanic, Dutch, and Scandinavian languages do use separate words to express this concept, and in those languages grand prince is understood as a distinct title (for a cadet of a dynasty) from grand duke (hereditary ruler ranking below a king). Some recent sources also use Archduke.

The title of grand prince was once used for the sovereign of a grand principality. The last titular grand principalities vanished in 1917 and 1918, the territories being united into other monarchies or becoming republics. Already at that stage, the grand principalities of Lithuania, Transylvania and Finland had been for centuries under rulers of other, bigger monarchies, so that the title of grand prince was superseded by the titles "king" and "emperor" there. Ivan IV of Moscow in the 16th century was the last sovereign to reign whose highest title was velikiy knyaz, until he assumed the rank of Tsar of Russia. "Velikiy knyaz" is a Russian title that is often translated as "grand prince" because there are no better equivalents in European languages. When Ivan IV's pre-tsarist title is referred to in English, however, it is usually as grand duke.

Velikiy knyaz is also a Russian courtesy title for members of the family of the Russian tsar (from the 17th century), although the people who held this title were not sovereigns.

Velikiy knyaz (Meaning closest to Grand Prince but was generally translated as Grand Duke in state documents written in Latin), used in the Slavic and Baltic languages, was the title of a medieval monarch who headed a more-or-less loose confederation whose constituent parts were ruled by lesser knyazs ( often translated as "princes" ) . Those great knyazs' (grand princes') title and position was at the time sometimes translated as king, though kings, princes, and dukes seemingly initially did not exist amongst proto-Slavs and Balts with Knyaz being a Germanic loanword adopted by tribal chieftains. Although, the Slavic knjaz and the Baltic kunigaikštis (nowadays usually translated as prince) are similar to kings in terms of ruling and duties. However, a velikiy knyaz (grand prince) was usually only primus inter pares within a dynasty, primogeniture not governing the order of succession. All knyazs (princes) of the family were equally eligible to inherit a crown (for example, succession might be through agnatic seniority or rotation). Often other members of the dynasty ruled some constituent parts of the monarchy/country. An established use of the title was in the Kievan Rus' and in the Grand Duchy of Lithuania (from the 14th century). Thus, Veliki Knjaz has been more like a regional high king (but without international recognition as such) than a "grand duke", at least, originally and was not subordinated to any other authority.^{[citation needed]}

Grand Prince (Hungarian: Nagyfejedelem) was the title used by contemporary sources to name the leader of the federation of the Hungarian tribes in the 10th century. Constantine VII mentioned Árpád in his book De Administrando Imperio as megas Turkias arkhon, while Bruno of Querfurt referred to Géza in his Sancti Adalberti Pragensis episcopi et martyris vita altera as Ungarorum senior magnus. It was used by Géza and his son and heir Stephen of Hungary.

In the Middle Ages, the Serbian veliki župan (велики жупан) was the supreme chieftain in the multi-tribal society. The title signifies overlordship, as the leader of lesser chieftains titled župan. It was used by the Serb rulers in the 11th and 12th centuries. In Greek, it was known as archizoupanos (ἄρχιζουπάνος), megazoupanos (μεγαζουπάνος) and megalos zoupanos (μεγάλος ζουπάνος).

In the 1090s, Vukan became the veliki župan in Raška (Rascia). Stefan Nemanja expelled his brother Tihomir in 1168 and assumed the title of veliki župan, as described in the Charter of Hilandar (и постави ме великог жупана). A Latin document used mega iupanus for King Stefan the First-Crowned (Stephanus dominus Seruie siue Rasie, qui mega iupanus). Afterwards, it was a high noble rank with notable holders such as Altoman Vojinović (fl. 1335–59).