Fulk of Anjou (Latin: Fulco, French: Foulque or Foulques; c. 1089/1092 – 13 November 1143), also known as Fulk the Younger, was the king of Jerusalem from 1131 until 1143 as the husband and co-ruler of Queen Melisende. Previously, he was the count of Anjou as Fulk V from 1109 to 1129. He had also been the count of Maine from 1110 to 1126 alongside his first wife, Countess Erembourg. His direct descendants were the rulers of the Angevin Empire and the Latin Kingdom of Jerusalem.

Fulk was born at Angers, between 1089 and 1092, the son of Count Fulk IV of Anjou and Bertrade de Montfort. In 1092, Bertrade deserted her husband, and bigamously married King Philip I of France. Fulk was thus raised at least partly at the French court. By 1106 Fulk's father had been forced to yield control of the county to his eldest son, Fulk's half-brother Geoffrey IV. But Geoffrey was killed that year by a crossbow bolt outside the castle of Candé, in theory returning his father to power and making Fulk the next in the line of succession. The chronicler Orderic Vitalis claims that the young Fulk was forced to do homage for Anjou to Philip I of France and was subsequently captured and held prisoner for a year by Duke William IX of Aquitaine. The earliest version of the Chronicles of the Deeds of the Counts of Anjou (Chronica de gestis consulum Andegavorum) may have been written in response to this crisis.

In 1109, Fulk's father died and Fulk V succeeded to the county of Anjou, ending the three-year crisis. In 1110 he married Countess Erembourg of Maine, cementing Angevin control over the County of Maine. In 1113, Erembourg gave birth to their son, the future Geoffrey V of Anjou.

Fulk was originally an opponent of King Henry I of England and a supporter of King Louis VI of France, but in 1119 he allied with Henry when he arranged for his daughter Matilda of Anjou to marry Henry's son William Adelin.

In 1119, possibly inspired by the news of the defeat of crusader forces at the Battle of the Field of Blood, and at a time when Pope Callixtus II was nearby in France, Fulk decided to take the cross as a crusader. During his visit to Jerusalem in 1120, he became associated with Knights Templar, possibly even joining them as a confrater. He became the first European prince to patronize the Templars, giving them an annual income of 30 pounds in the money of Anjou. He promised to maintain one hundred knights in the Holy Land for a year.

By the 1120s, concern was growing about the succession to King Baldwin II of Jerusalem, who had only daughters, the eldest being Melisende. Many factors argued in favor of Fulk's candidacy: he had visited Jerusalem and supported the kingdom and the Templars; his son Geoffrey had come of age in 1126; and his wife Erembourg died in the same year. The assassination of Count Charles the Good of Flanders in 1127, who had likewise visited Jerusalem in his youth and was a popular contender, made Fulk the obvious choice.

In 1127, Baldwin dispatched an embassy to Fulk led by two noblemen, William of Bures, prince of Galilee and Guy Brisebarre, and the Master and co-founder of the Knights Templar Hugh of Payns. The embassy was tasked with finding a husband for Melisende and raising an army for an attack on Damascus. After consulting with his barons, Baldwin had decided to offer Melisende's hand in marriage to Fulk, with the promises that they should be married within 50 days of Fulk's arrival in the Latin East and that Fulk could expect to hold the kingdom after Baldwin's death. In Spring 1128, the embassy reached Anjou. Hans Eberhard Mayer has reconstructed the extensive negotiations that must have taken place between Fulk and the ambassadors, which he believes led Baldwin II to treat both Fulk and Melisende as the "heir of the king" (heres regni) to forestall any challenge to their succession. By 31 May, Fulk seems to have accepted their offer, for he took the cross on that day in Le Mans. He spent the next year setting his affairs in order, transferring lordship over Anjou and Maine to his son Geoffrey, who had married Matilda, daughter of King Henry I of England. Fulk apparently did not relinquish the title of "count of Anjou", perhaps as insurance in case the Jerusalem plan did not succeed. In about March 1129, Fulk departed for Jerusalem accompanied by a number of crusaders recruited from Anjou and the surrounding region. They arrived in the East in May of that year and Fulk and Melisende were married on the Feast of Pentecost, 2 June 1129. As Melisende's dowry, Baldwin II presented Fulk with the cities of Acre and Tyre. That winter, Fulk and the army recruited in Europe by Hugh of Payns attacked Damascus.

Baldwin II of Jerusalem died on 21 August 1131. The coronation of Fulk and Melisende took place on 14 September, the Feast of the Exaltation of the Holy Cross, in the Church of the Holy Sepulcher. It was the first time that a ruler of Jerusalem had been crowned in this way. On the occasion of his coronation, the Egyptian ruler Kutayfat sent Fulk an ivory object described as "the ivory tau". Fulk subsequently sent the ivory tau back to his palace at Angers with instructions that it should be used to ceremonially receive counts of Anjou.