The Wægmundings were a prominent probably Swedish clan (an ätt, see Norse clans) in Beowulf. A name such as Wægmunding meant "belongs to Wægmund", i.e. they were the descendants of a man named Wægmund. This was the normal way of naming a Germanic clan (see e.g. Sigurd the Völsung, descendant of king Völsung), Folkung (descendants of Folke) and Yngling (descendants of Yngvi-Freyr).
Members:
The story of this clan in Beowulf is that Ecgþeow slew a man, Heaðolaf, from another clan, the Wulfings (probably the rulers of the less known East Geats). As the Wægmundings would not or could not pay the expected wergild, Ecgtheow was banished and sought refuge among the Danes. The Danish king Hrothgar paid the wergild and had Ecgþeow swear an oath. Later, Ecgþeow served the Geats and distinguished himself enough to marry the Geatish king Hreðel's daughter, with whom he had the son Beowulf.
During the Swedish-Geatish wars, Ecgþeow's close relative, Weohstan, fought on the Swedish side for Onela, and killed Onela's nephew Eanmund. The fact that these characters are described as Wægmundings explains why the Swedish warrior Wiglaf became the companion of Beowulf although his father had fought against the Geats. Since Ecgþeow, Beowulf's father, was a close relative of Weohstan, Wiglaf's father, it is not surprising that Wiglaf (after his father's death) joined his relative Beowulf in Geatland, and that Beowulf assumed responsibility for the young Swede.