Geoffrey V (24 August 1113 – 7 September 1151), called the Fair (French: le Bel), Plantagenet, and of Anjou, was the count of Anjou and Maine by inheritance from 1129, and also duke of Normandy by his marriage claim and conquest, from 1144.

Geoffrey married Empress Matilda, daughter of Henry I, king of England and duke of Normandy. Geoffrey and Matilda's marriage led, through their son Henry II, to the 300-year long reign of the Plantagenet dynasty in England. Although it was never his family name or last name, "Plantagenet" was taken for the dynasty from Geoffrey's epithet, long after his death. Geoffrey's ancestral domain of Anjou in north central France gives rise to the name Angevin, and what modern historians name as the Angevin Empire in the 12th century.

Geoffrey was the elder son of Fulk V of Anjou and Ermengarde of Maine. The chronicler John of Marmoutier described Geoffrey as handsome, red haired, jovial, and a great warrior. King Henry I of England, having heard reports on Geoffrey's talents and prowess, sent legates to Anjou to negotiate a marriage between his 25-year-old daughter Matilda and Geoffrey. Consent was obtained from both parties, and on 10 June 1128 King Henry, who was also the duke of Normandy, knighted the 15-year-old Geoffrey in preparation for the wedding. Geoffrey of Anjou perhaps received the nickname (much later used for the royal dynasty that resulted from this marriage) from the yellow sprig of broom blossom (genêt is the French name for the planta genista, or broom shrub) he wore in his hat.

Geoffrey and Matilda's marriage took place in 1128. The marriage was meant to seal a lasting peace between England, Normandy and Anjou. She was eleven years older than Geoffrey and very proud of her status as dowager empress (as opposed to being a mere countess), which she kept for the remainder of her life. Their relationship was a stormy but happy one with frequent long separations. Matilda returned to her father's court after only a few months. Upon intervention from King Henry I, Matilda returned to Geoffrey, and Matilda became pregnant with their first son, the future King Henry II, not long after. They had three sons Henry, Geoffrey and William.

The year after the marriage, Geoffrey's father, Fulk, left on crusade for Jerusalem (where he was to later become king), leaving Geoffrey behind as count of Anjou.

When his father in law, King Henry I of England, died in 1135, Geoffrey supported Matilda in entering Normandy to claim her inheritance. The border districts submitted to her, but in England her first cousin Stephen of Blois had been crowned king, supported by a number of barons after claims that Henry I had changed his mind on his deathbed in regard to his heir. Barons in Normandy soon followed suit, or were in a large majority the same barons as in England. There were a number that supported Matilda, her claim to the throne, and the two vows that they had taken at the request of Henry, for her to be his heir. The following year, Geoffrey gave Ambrieres, Gorron, and Chatilon-sur-Colmont to Juhel de Mayenne, on condition that he help obtain the inheritance of Geoffrey's wife.

In 1139, Matilda landed in England with 140 knights, where she was besieged at Arundel Castle by King Stephen. In the Anarchy which ensued, Stephen was captured at Lincoln in February 1141, and imprisoned at Bristol. A legatine council of the English church held at Winchester in April 1141 declared Stephen deposed and proclaimed Matilda "Lady of the English".

During 1142 and 1143, Geoffrey secured all of Normandy west and south of the Seine, and, on 14 January 1144, he crossed the Seine and entered Rouen. He assumed the title of Duke of Normandy in the summer of 1144. In 1144, he founded an Augustine priory at Château-l'Hermitage in Anjou. Geoffrey held the duchy until 1149, when he and Matilda conjointly ceded it to their son, Henry, which cession was formally ratified by King Louis VII of France the following year.