The Jagiellonian dynasty (; ; ; ), also known as the House of Jagiellon () or simply the Jagiellons (; ; ), was a Polish cadet branch of the Lithuanian ducal dynasty of Gediminids. The Jagiellons reigned in several European countries between the 14th and 16th centuries. Members of the dynasty were Kings of Poland (1386–1572), Grand Dukes of Lithuania (1377–1392 and 1440–1572), Kings of Hungary (1440–1444 and 1490–1526), and Kings of Bohemia and imperial electors (1471–1526).

The dynasty originated with Jogaila, the Grand Duke of Lithuania, who was baptized as Ladislaus () in 1386, which paved the way to his ensuing marriage to the Queen Regnant Jadwiga of Poland, resulting in his ascension to the Crown of the Kingdom of Poland as Władysław II Jagiełło, and the effective promotion of his branch to a royal dynasty. The personal union between the Kingdom of Poland and the Grand Duchy of Lithuania (converted in 1569 with the Treaty of Lublin into the Polish–Lithuanian Commonwealth) is the reason for the common appellation "Poland–Lithuania" in discussions about the area from the Late Middle Ages onward. One Jagiellon, Władysław III of Poland, briefly ruled both Poland and Hungary (1440–1444), and two others ruled both Bohemia and Hungary (1490–1526) and then continued in the distaff line as a branch of the House of Habsburg.

The Polish "Golden Age", the period of the reigns of Sigismund I and Sigismund II, the last two Jagiellonian kings, or more generally the 16th century, is most often identified with the rise of the culture of Polish Renaissance. The cultural blossoming had its material base in the prosperity of the elites, both the landed nobility and urban patriciate at such centers as Kraków and Gdańsk. The Jagiellons were polyglots and per historical evidence Casimir IV Jagiellon and his son Saint Casimir possibly were the last Jagiellons who spoke in their patrilineal ancestors' Lithuanian language; however, even the last patrilineal Jagiellonian monarch Sigismund II Augustus maintained two separate and equally lavish Lithuanian-speaking and Polish-speaking royal courts in Lithuania's capital Vilnius.

Name The name comes from Jogaila (), the first Grand Duke of Lithuania to become King of Poland. In Polish, the dynasty is known as and the patronymic form: ; in Lithuanian it is called , in Belarusian (), in Ukrainian (), in Hungarian , in Croatian , in Slovak , and in Czech , as well as or in Latin. Etymologically, the name Jogaila means "strong rider", from the Lithuanian words (to ride) and (strong, powerful).

Pre-dynasty background The rule of Piasts, the earlier Polish ruling house (c. 962–1370) had ended with the death of King Casimir III the Great. Gediminids, the immediate predecessors of the first Jagiellonian, were rulers of medieval Lithuania with the title of Grand Duke. Their realm, the Grand Duchy of Lithuania, was chiefly inhabited by Lithuanians and Ruthenians.

Jogaila, the eponymous first ruler of the Jagiellonian dynasty, started as the Grand Duke of Lithuania. As a result of the Union of Krewo he then converted to Christianity and married the 12-year-old Queen Jadwiga of Poland (daughter of King Louis I of Hungary from the Angevins Dynasty). Thereby he became King of Poland as her co-ruler.Borkowska, Urszula (2012). Dynastia Jagiellonów w Polsce (in Polish). PWN. . Jadwiga died in 1399 and, as her and Jogaila's daughter, Princess Elizabeth, died as infant, Jogaila lost inheritance rights to Polish crown for his future descendants, but he remained the King of Poland as elected ruler. He eventually went to have 4 more children and started a Jagiellonian dynasty, whose members continued to be elected as monarchs of Poland.

Kingdom of Poland

Jogaila and Władysław III

Polish–Lithuanian union

In 1385 the Union of Krewo was signed between Queen Jadwiga of Poland and Jogaila, the Grand Duke of Lithuania, the last pagan state in Europe. The act arranged for Jogaila's baptism (after which Jogaila was known in Poland by his baptismal name Władysław, and the Polish version of his Lithuanian name, Jagiełło) (Zamoyski, the Polish Way) and for the couple's marriage and constituted the beginning of the Polish–Lithuanian union. The Union strengthened both nations in their shared opposition to the Teutonic Knights and the growing threat of the Grand Duchy of Moscow. Uniquely in Europe, the union connected two states geographically located on the opposite sides of the great civilizational divide between the Western or Latin, and the Eastern or Byzantine worlds.Krzysztof Baczkowski – Dzieje Polski późnośredniowiecznej (1370–1506) (History of Late Medieval Poland (1370–1506)), p. 55; Fogra, Kraków 1999,

The intention of the Union was to create a common state under Władysław II Jagiełło, but the Polish ruling oligarchy's idea of incorporation of Lithuania into Poland turned out to be unrealistic. There would be territorial disputes and warfare between Poland and Lithuania or Lithuanian factions; the Lithuanians at times had even found it expedient to conspire with the Teutonic Knights against the Poles. Geographic consequences of the dynastic union and the preferences of the Jagiellonian kings accelerated the process of reorientation of Polish territorial priorities to the east. The political influence of the Jagiellonian kings was diminishing during this period, which was accompanied by the ever-increasing role in central government and national affairs of landed nobility. The royal dynasty, however, had a stabilizing effect on Poland's politics. The Jagiellonian Era is often regarded as a period of maximum political power, great prosperity, and in its later stage, the Golden Age of Polish culture.

Struggle with the Teutonic Knights

The Great War of 1409–1411, precipitated by the Lithuanian uprising in the Order controlled Samogitia, included the Battle of Grunwald (Tannenberg), where the Polish and Lithuanian armies completely defeated the Teutonic Knights. The offensive that followed lost its impact with the ineffective siege of Malbork (Marienburg). The failure to take the fortress and eliminate the Teutonic (later Prussian) state had for Poland dire historic consequences in the 18th, 19th and 20th centuries. The Peace of Thorn (1411) had given Poland and Lithuania rather modest territorial adjustments, including Samogitia. Afterwards there were negotiations and peace deals that didn't hold, more military campaigns and arbitrations. One attempted, unresolved arbitration took place at the Council of Constance.

Polish–Hungarian union During the Hussite Wars (1420–1434), Jagiełło, Vytautas and Sigismund Korybut were involved in political and military maneuvering concerning the Czech crown, offered by the Hussites first to Jagiełło in 1420. Zbigniew Oleśnicki became known as the leading opponent of a union with the Hussite Czech state.

The Jagiellonian dynasty was not entitled to automatic hereditary succession, as each new king had to be approved by nobility consensus. Władysław Jagiełło had three sons (two of whom survived infancy) late in life from his last wife, Sophia of Halshany. In 1430 the nobility agreed to the succession of the future Władysław III, only after the King gave in and guaranteed the satisfaction of their new demands. In 1434 the old monarch died and his minor son Władysław was crowned; the Royal Council led by Bishop Oleśnicki undertook the regency duties. In 1438 the Czech anti-Habsburg opposition, mainly Hussite factions, offered the Czech crown to Jagiełło's younger son Casimir IV. The idea, accepted in Poland over Oleśnicki's objections, resulted in two unsuccessful Polish military expeditions to Bohemia.

After Vytautas' death in 1430 Lithuania became embroiled in internal wars and conflicts with Poland. Casimir IV, sent as a boy by Władysław III on a mission there in 1440, was surprisingly proclaimed by the Lithuanians as a Grand Duke of Lithuania, and he stayed in Lithuania.

Oleśnicki gained the upper hand again and pursued his long-term objective of Poland's union with Hungary. At that time the Ottoman Empire embarked on a new round of European conquests and threatened Hungary, which needed the powerful Polish–Lithuanian ally. In 1440 Władysław III assumed the Hungarian throne. Influenced by Julian Cesarini, the young king led the Hungarian army against the Ottomans in 1443 and again in 1444. During battle of Varna Władysław III disappeared and is presumed to be killed at the battlefield; he was eventually assumed to be deceased in Poland in 1445, when Polish throne was given to his only living brother, the Grand Duke of Lithuania Casimir, who was ultimately crowned two years later.Besala, Jerzy (2006). Małżeństwa królewskie. Jagiellonowie (in Polish). Bellona Muza. . Beginning toward the end of Jagiełło's life, Poland was practically governed by a magnate oligarchy led by Oleśnicki. The rule of the dignitaries was actively opposed by various szlachta groups. Their leader Spytek of Melsztyn was killed during an armed confrontation in 1439, which allowed Oleśnicki to purge Poland of the remaining Hussite sympathizers and pursue his other objectives without significant opposition.

Casimir IV Jagiellon

Casimir IV Jagiellon was the third and youngest son of King Władysław II Jagiełło and his fourth wife, Sophia of Halshany. His father was already 65 at the time of Casimir's birth, and his brother Władysław III, three years his senior, was expected to become king before his majority. Strangely, little was done for his education; he was never taught Latin, nor was he trained for the responsibilities of office, despite the fact he was the only brother of the rightful sovereign. He often relied on his instinct and feelings and had little political knowledge, but shared a great interest in the diplomacy and economic affairs of the country. Throughout Casimir's youth, Bishop Zbigniew Oleśnicki was his mentor and tutor; however, the cleric felt a strong reluctance towards him, believing that he would be an unsuccessful monarch following Władysław's death.