Beowulf describes a dark and terrifying world, in which the victories of light over darkness are small, contingent, and temporary. At the beginning of the epic, Hrothgar's mead hall is the one point of light and celebration, but even that is not safe. Hrothgar has no way of protecting his people until Beowulf arrives.

It would not be much of an exaggeration to say that all the characters in Beowulf are alienated most of the time. Beowulf is in perpetual isolation because is is a great hero. Achilles, Aeneas, and even Odysseus are similarly alone, though they inhabit less frightening and desolate worlds. The Danes are alienated from their environment, vainly trying to create a small, precarious space for humanity in the midst of the darkness. Modern audiences also notice the alienation and loneliness of Grendel. Though the poet seems to have regarded the monster as purely evil and undeserving of sympathy, recent re-imaginings such as John Gardner's novel, Grendel, have focused on how alienated he would have felt upon hearing the rejoicing in Heorot.

The end of the poem is a triumph of alienation. Wiglaf predicts that the Geats who left their king alone to die will soon be wiped out. Beowulf was a unique hero, the only man who could save the Danes or the Geats. After his death, it will not be long before darkness defeats them.