Isabella II (Old French: Ysabel; 1212 – May 1228), sometimes called Isabella of Brienne and erroneously Yolanda, was the queen of Jerusalem who reigned from 1212 to 1228. She was the daughter and successor of Maria of Montferrat, who died shortly after giving birth to her. Like her mother, Isabella died young before she could make an impression on politics.

Isabella's father, John of Brienne, ruled during her long minority; while he continued to regard himself as king for life, his opponents insisted that he was merely regent for Isabella. In 1223 John arranged for her to marry Emperor Frederick II, king of Sicily. A proxy wedding was held in the Kingdom of Jerusalem in August 1225, followed by Isabella's coronation as queen of Jerusalem. She then promptly departed for the Kingdom of Sicily, where she married Frederick in person. The marriage made her queen of Sicily and empress of the Holy Roman Empire. Defying his agreement with her father, Frederick declared himself king of Jerusalem immediately after their wedding and seized control of her kingdom. He sidelined Isabella, whose role in government was minimal. Her father's supporters alleged that Frederick abused her. She died shortly after giving birth to her only son, Conrad II, who succeeded her under Frederick's tutelage.

Isabella was born in late 1212 in the Kingdom of Jerusalem, then a rump state that did not include the city of Jerusalem. She was the only child of the queen of Jerusalem, Maria of Montferrat, who died from childbirth complications. The infant was named after Maria's mother and predecessor, Queen Isabella I. Isabella II thus inherited the kingdom within days of her birth, but the situation was unprecedented because her father, John of Brienne, was still alive. He had become king when he married Maria and expected to keep the crown for his lifetime. While most nobles were apparently willing to still recognize him as king, a faction aligned with the powerful Ibelin family considered John's reign to be over and held that, at best, he could rule only as regent on Isabella's behalf. In a letter of condolence on Maria's death, Pope Innocent III promised to John that he would support him and Isabella, and further wrote to Prince Bohemond IV of Antioch and the clergy of the Kingdom of Jerusalem to instruct them to do the same.

Isabella I had left five daughters from three marriages: Maria of Montferrat, Alice and Philippa of Champagne, and Sibylla and Melisende of Cyprus. Alice, then queen of Cyprus, was the eldest of Isabella II's half-aunts and thus her heir presumptive. Because Alice and Philippa held a strong claim to the County of Champagne, Blanche of Navarre, the ruling countess, pressed for an inquiry into the validity of Isabella I's marriages, hoping to weaken the sisters' position by questioning their legitimacy. Her argument carried weight: Isabella I's childless first marriage to Humphrey IV of Toron had been annulled under dubious circumstances, and Humphrey lived throughout her two subsequent unions. Maria, Isabella II's mother, was herself the child of one of these disputed marriages. Nevertheless, Pope Innocent III refused to pursue the case, likely wary of the political consequences in the Latin East, and Isabella II's claim to the throne of Jerusalem stood unchallenged.

Isabella's father, King John, remarried in 1214. His second wife, Stephanie of Armenia, died in 1220. According to the Chronicle of Ernoul and Bernard the Treasurer, she had tried to poison Isabella; when John heard about it, he beat her so hard that–rumor had it–she died from it. The historians Ludwig Böhm and Guy Perry dismiss this account. In 1221, Isabella started giving her consent to her father's acts. In the only surviving such document, she is referred to simply as the king's daughter, in contrast to her mother, Maria, who had been titled "the honourable lady of the kingdom" prior to her coronation. The lack of reference to her status may reflect John's insistence that he was the reigning king rather than merely regent for Isabella.

In late 1222, after the failure of the Fifth Crusade, King John travelled to Europe to solicit support for the kingdom. Although she was only nine or ten, John took this opportunity to seek a husband for Isabella. The objective was to find a powerful leader who could summon substantial Western aid for the beleaguered kingdom. John nevertheless continued to regard the kingship as his for life and assumed that Isabella's future husband would only take up rule after John's death.

At a conference in Ferentino in March 1223, Isabella was proposed as a bride for Frederick II, the recently widowed emperor of the Holy Roman Empire and king of Sicily, who was preparing to lead the next crusade. The match was suggested by Hermann of Salza, grand master of the Teutonic Knights. Although John welcomed the prospect of such a distinguished alliance, he wavered until Hermann promised him the kingdom's government for life. Pope Honorius III may also have encouraged the union since he soon issued a dispensation permitting the couple to marry despite being third cousins. Frederick then persuaded John to remain in Europe and join the forthcoming crusade.

At a conference in San Germano in July 1225, Frederick swore that he would depart on crusade by 15 August 1227 and received John's permission to marry Isabella without delay. A fleet was promptly sent to fetch her. Count Henry of Malta and James, archbishop-elect of Capua, reached Acre with fourteen imperial galleys in August. Isabella was married by proxy in the Cathedral of the Holy Cross, with James standing in for Frederick. She was then taken to Tyre and crowned queen of Jerusalem by the Latin patriarch of Jerusalem, Ralph of Mérencourt. The ceremony was attended by the leading nobles, including the constable and bailiff, Odo of Montbéliard; the archbishop of Tyre, Simon of Maugastel; and even the lord of Caesarea, Walter III, who had once been her father's opponent. The Ibelins, however, were absent. After a fortnight of celebrations, Isabella embarked together with the archbishop of Tyre and her cousin the lord of Sidon, Balian Grenier. According to the Gestes des Chiprois, a pro-Ibelin chronicle, Isabella made a stop at Cyprus, where she met with her aunt Queen Alice.