structural:scholar_edition, structural:expansion
European relations

The West Saxon court had connections with the Carolingians going back to the marriage between Æthelstan's great-grandfather Æthelwulf and Judith, daughter of the king of West Francia (and future Holy Roman Emperor) Charles the Bald, as well as the marriage of Alfred the Great's daughter Ælfthryth to Judith's son by a later marriage, Baldwin II, Count of Flanders. One of Æthelstan's half-sisters, Eadgifu, married Charles the Simple, king of the West Franks, in the late 910s. He was deposed in 922, and Eadgifu sent their son Louis to safety in England. By Æthelstan's time the connection was well established, and his coronation was performed with the Carolingian ceremony of anointment, probably to draw a deliberate parallel between his rule and Carolingian tradition. His "crowned bust" coinage of 933–938 was the first Anglo-Saxon coinage to show the king crowned, following Carolingian iconography.

Like his father, Æthelstan was unwilling to marry his female relatives to his own subjects, so his sisters either entered nunneries or married foreign husbands. This was one reason for his close relations with European courts, and he married several of his half-sisters to European nobles in what historian Sheila Sharp called "a flurry of dynastic bridal activity unequalled again until Queen Victoria's time". Another reason lay in the common interest on both sides of the Channel in resisting the threat from the Vikings, while the rise in the power and reputation of the royal house of Wessex made marriage with an English princess more prestigious to European rulers. In 926 Hugh, Duke of the Franks, sent Æthelstan's cousin, Adelolf, Count of Boulogne, on an embassy to ask for the hand of one of Æthelstan's sisters. According to William of Malmesbury, the gifts Adelolf brought included spices, jewels, many swift horses, a crown of solid gold, the sword of Constantine the Great, Charlemagne's lance, and a piece of the Crown of Thorns. Æthelstan sent his half-sister Eadhild to be Hugh's wife.

Æthelstan's most important European alliance was with the new Liudolfing dynasty in East Francia. The Carolingian dynasty of East Francia had died out in the early tenth century, and its new Liudolfing king, Henry the Fowler, was seen by many as an arriviste. He needed a royal marriage for his son to establish his legitimacy, but no suitable Carolingian princesses were available. The ancient royal line of the West Saxons provided an acceptable alternative, especially as they (wrongly) claimed descent from the seventh-century king and saint, Oswald, who was venerated in Germany. In 929 or 930 Henry sent ambassadors to Æthelstan's court seeking a wife for his son, Otto, who later became Holy Roman Emperor. Æthelstan sent two of his half-sisters, and Otto chose Eadgyth. Fifty years later, Æthelweard, a descendant of Alfred the Great's older brother, addressed his Latin version of the Anglo-Saxon Chronicle to Mathilde, Abbess of Essen, who was Eadgyth's granddaughter, and had apparently requested it. The other sister, whose name is uncertain, was married to a prince from near the Alps who has not definitely been identified.

In early medieval Europe, it was common for kings to act as foster-fathers for the sons of other kings. Æthelstan was known for the support he gave to dispossessed young royalty. In 936 he sent an English fleet to help his foster-son, Alan II, Duke of Brittany, to regain his ancestral lands, which had been conquered by the Vikings. In the same year he assisted the son of his half-sister Eadgifu, Louis, to take the throne of West Francia, and in 939 he sent another fleet that unsuccessfully attempted to help Louis in a struggle with rebellious magnates. According to later Scandinavian sources, he helped another possible foster-son, Hakon, son of Harald Fairhair, king of Norway, to reclaim his throne, and he was known among Norwegians as "Æthelstan the Good".

Æthelstan's court was perhaps the most cosmopolitan of the Anglo-Saxon period. The close contacts between the English and European courts ended soon after his death, but descent from the English royal house long remained a source of prestige for continental ruling families. According to Frank Stenton in his history of the period, Anglo-Saxon England, "Between Offa and Cnut there is no English king who played so prominent or so sustained a part in the general affairs of Europe."

Foreign contemporaries described him in panegyrical terms. The French chronicler Flodoard described him as "the king from overseas", and the Annals of Ulster as the "pillar of the dignity of the western world". Some historians take a similar view. Michael Wood titled an essay, "The Making of King Aethelstan's Empire: an English Charlemagne?", and described him as "the most powerful ruler that Britain had seen since the Romans". In the view of Veronica Ortenberg, he was "the most powerful ruler in Europe" with an army that had repeatedly defeated the Vikings; continental rulers saw him as a Carolingian emperor, who "was clearly treated as the new Charlemagne". She wrote:

Wessex kings carried an aura of power and success, which made them increasingly powerful in the 920s, while most Continental houses were in military trouble and engaged in internecine warfare. While the civil wars and the Viking attacks on the Continent had spelled the end of unity of the Carolingian empire, which had already disintegrated into separate kingdoms, military success had enabled Æthelstan to triumph at home and to attempt to go beyond the reputation of a great heroic dynasty of warrior kings, in order to develop a Carolingian ideology of kingship.