Edmund I or Eadmund I (920/921 – 26 May 946) was King of the English from 27 October 939 until his death. He was the elder son of King Edward the Elder and his third wife, Queen Eadgifu, and a grandson of King Alfred the Great. When Edward died in 924 he was succeeded by his eldest son, Edmund's half-brother Æthelstan, who died childless in 939. Edmund then became king. He had two sons, Eadwig and Edgar, by his first wife Ælfgifu, and none by his second wife Æthelflæd. His sons were young children when he was killed in a brawl with an outlaw at Pucklechurch in Gloucestershire, and he was succeeded by his younger brother Eadred, who died in 955 and was followed by Edmund's sons in succession.

Æthelstan had succeeded as the king of England south of the Humber and he became the first king of all England when he conquered Viking-ruled York in 927, but after his death Anlaf Guthfrithson was accepted as king of York and extended Viking rule to the Five Boroughs of north-east Mercia. Edmund was initially forced to accept the reverse, the first major setback for the West Saxon dynasty since Alfred's reign, but he was able to recover his position following Anlaf's death in 941. In 942 Edmund took back control of the Five Boroughs and in 944 he regained control over the whole of England when he expelled the Viking kings of York. Eadred had to deal with further revolts when he became king and York was not finally conquered until 954. Æthelstan had achieved a dominant position over other British kings and Edmund maintained this, perhaps apart from Scotland. The north Welsh king Idwal Foel may have allied with the Vikings as he was killed by the English in 942. The British kingdom of Strathclyde may also have sided with the Vikings as Edmund ravaged it in 945 and then ceded it to Malcolm I of Scotland. Edmund also continued his brother's friendly relations with Continental rulers, several of whom were married to his half-sisters.

Edmund inherited his brother's interests and leading advisers, such as Oda, whom he appointed Archbishop of Canterbury in 941, Æthelstan Half-King, ealdorman of East Anglia and Ælfheah the Bald, Bishop of Winchester. Government at the local level was mainly carried on by ealdormen, and Edmund made substantial changes in personnel during his reign, with a move from Æthelstan's main reliance on West Saxons to a greater prominence of men with Mercian connections. Unlike the close relatives of previous kings, his mother and brother attested many of Edmund's charters, suggesting a high degree of family cooperation. Edmund was also an active legislator, and three of his codes survive. Provisions include ones which attempt to regulate feuds and emphasise the sanctity of the royal person.

The major religious movement of the tenth century, the English Benedictine Reform, reached its peak under Edgar, but Edmund's reign was important in its early stages. He appointed Dunstan abbot of Glastonbury, where he was joined by Æthelwold. They were to be two of the leaders of the reform and they made the abbey the first important centre for disseminating it. Unlike the circle of his son Edgar, Edmund did not take the view that Benedictine monasticism was the only worthwhile religious life and he also patronised unreformed (non-Benedictine) establishments.