The Norman Conquest (or the Conquest) was the 11th-century invasion and occupation of England by an army made up of thousands of Normans, Bretons, Flemish, and French troops, all led by the Duke of Normandy, later styled William the Conqueror.

William's claim to the English throne derived from his familial relationship with the childless Anglo-Saxon king Edward the Confessor, who may have encouraged William's hopes for the throne. Edward died in January 1066 and was succeeded by his brother-in-law Harold Godwinson. The Norwegian king Harald Hardrada invaded northern England in September 1066 and was victorious at the Battle of Fulford on 20 September, but Godwinson's army defeated and killed Hardrada at the Battle of Stamford Bridge on 25 September. Three days later on 28 September, William's invasion force of thousands of men and hundreds of ships landed at Pevensey in Sussex in southern England. Harold marched south to oppose him, leaving a significant portion of his army in the north. Harold's army confronted William's invaders on 14 October at the Battle of Hastings. William's force defeated Harold, who was killed in the engagement, and William became king.

Although William's main rivals were gone, he still faced rebellions over the following years and was not secure on the English throne until after 1072. The lands of the resisting English elite were confiscated; some of the elite fled into exile. To control his new kingdom, William granted lands to his followers and built castles commanding military strongpoints throughout the land. The Domesday Book, a manuscript record of the "Great Survey" of much of England and parts of Wales, was completed by 1086. Other effects of the conquest included the court and government, the introduction of the Norman language as the language of the elites, and changes in the composition of the upper classes, as William enfeoffed lands to be held directly from the king. More gradual changes affected the agricultural classes and village life: the main change appears to have been the formal elimination of slavery, which may or may not have been linked to the invasion. There was little alteration in the structure of government, as the new Norman administrators took over many of the forms of Anglo-Saxon government.

William I (c. 1028 – 9 September 1087), usually known as William the Conqueror and sometimes William the Bastard, was the first Norman monarch of England, reigning from 1066 until his death in 1087. A descendant of Rollo, he was Duke of Normandy from 1035 onward. By 1060, following a long struggle to establish his throne, his hold on Normandy was secure. In 1066, following the death of Edward the Confessor, William invaded England, leading an army of Normans to victory over the Anglo-Saxon forces of Harold Godwinson at the Battle of Hastings, and suppressed subsequent English revolts in what has become known as the Norman Conquest. The rest of his life was marked by struggles to consolidate his hold over England and his continental lands, and by difficulties with his eldest son, Robert Curthose.

William was the son of the unmarried Duke Robert I of Normandy and his mistress Herleva. His illegitimate status and his youth caused some difficulties for him after he succeeded his father, as did the anarchy which plagued the first years of his rule. During his childhood and adolescence, members of the Norman aristocracy battled each other, both for control of the child duke, and for their own ends. In 1047, William was able to quash a rebellion and begin to establish his authority over the duchy, a process that was not complete until about 1060. His marriage in the 1050s to Matilda of Flanders provided him with a powerful ally in the neighbouring county of Flanders. By the time of his marriage, William was able to arrange the appointment of his supporters as bishops and abbots in the Norman church. His consolidation of power allowed him to expand his horizons, and he secured control of the neighbouring county of Maine by 1062.

In the 1050s and early 1060s, William became a contender for the throne of England held by the childless Edward the Confessor, his first cousin once removed. There were other potential claimants, including the powerful English earl Harold Godwinson, whom Edward named as king on his deathbed in January 1066. Arguing that Edward had previously promised the throne to him and that Harold had sworn to support his claim, William built a large fleet and invaded England in September 1066. He decisively defeated and killed Harold at the Battle of Hastings on 14 October 1066. After further military efforts, William was crowned king on Christmas Day, 1066, in London. He made arrangements for the governance of England in early 1067 before returning to Normandy. Several unsuccessful rebellions followed, but William's hold was mostly secure on England by 1075, allowing him to spend the majority of his reign in continental Europe.

William's final years were marked by difficulties in his continental domains, troubles with his son, Robert, and threatened invasions of England by the Danes. In 1086, he ordered the compilation of the Domesday Book, a survey listing all the land-holdings in England along with their pre-Conquest and current holders. He died in September 1087 while leading a campaign in northern France, and was buried in Caen. His reign in England was marked by the construction of castles, settling a new Norman nobility on the land, and change in the composition of the English clergy. He did not try to integrate his various domains into one empire but continued to administer each part separately. His lands were divided after his death: Normandy went to Robert, and England went to his second surviving son, William Rufus.