Hiccup (Jay Baruchel) is a young Viking whose village is continually pestered by dragons. Every citizen's primary concern is learning how to kill the beasts, which regularly raid the place for food.
Hiccup is a disappointment to his father, the mighty Stoick (Gerard Butler), because he lacks the brawn and temperament necessary to hunt dragons.
While dad is off on an expedition to find the dragons' nest, which Vikings have sought for centuries and never found, Hiccup takes training courses from an eager old veteran named Gobber (Craig Ferguson). His classmates are a handful of other kids his age, who tease him for his weakness while bragging about their own dragon-killing prowess.
But in a meadow outside the village, Hiccup comes across a smallish dragon, black and sleek and unable to fly because of a tail injury. Given the opportunity to kill the beast, his first! Hiccup finds he cannot do it. The poor thing is as scared as he is.
A bond develops. Hiccup and the dragon, dubbed Toothless, become friends. Hiccup discovers that most of the Vikings' information on dragons is wrong. Until now, no one has ever spent enough time with one to learn anything other than how to kill it. Perhaps there is a way for Vikings and dragons to co-exist peacefully? Perhaps this has all just been a big misunderstanding?