Beowulf is an epic poem that simply chronicles the adventures of its namesake, as he battles various and sundry fell beasts. It is divided into three major parts, or battles: Grendel, Grendel's mother in the lake, and the dragon.
The beginning of the poem details the trials and tribulations of Hrothgar, king of the Danes; his beautiful hall Heorot is besieged by the demon Grendel. When Beowulf hears of this, he comes straightaway to Heorot and battles the monster, ultimately ripping its arms off. The resulting celebration is cut short when Grendel's mother, in a frenzy of grief, kills several of the revelers. Beowulf then follows her to a lake, where he descends into the depths and battles her with a sword he finds there, killing her.
The third part of the tale jumps forward many years. Beowulf is now an ageing king of his people, and a dragon is enraged and begins to ravage the land. Good king that he is, Beowulf meets the dragon in battle, defeating it but receiving a death-blow in turn. The funeral of this great hero marks the tragic end of the tale.
One of the most remarkable facets of Beowulf, and one of the reasons for its popularity, is its use of kennings, or extreme personification. For example, rather than use the term "ocean," the poem would use "swan-road;" rather than "water-churning boat," "foamy-necked floater." This makes for an extremely interesting read, as many things are referred to in a roundabout way.