A young Viking boy by the name of Hiccup (voice of Jay Baruchel of THE SORCERER'S APPRENTICE) doesn't fit in with his village. They are all warriors and want to kill dragons, while he simply wants to invent things. In fact, he invents a catapult that manages to bring down a rare form of dragon, something no one else has been able to do. He goes out the next day and finds it wrapped up in the netting--but instead of killing it he sets it free. It senses he's a friend so the creature doesn't eat him on the spot. Hiccup sees that the creature can no longer fly, as it's missing a fin on its tail, which keeps it off balance. So he designs an artificial fin, which he attaches, and is able to ride the dragon. While all this is secretly happening, the other youths at the village are undergoing dragon-slaying classes. Amongst them is teenaged girl Astrid, who Hiccup has a crush on. When Hiccup participates he's able to utilize information he's learned from his own dragon, like how to scare them with eels or put them to sleep with a touch. Eventually Hiccup shares his secret with Astrid and takes her for a wild flight, which leads them to the secret island where all the different dragons live. Its there that they discover that the lizards are under rule of a gigantic beast--and that's where the majority of their food goes, to sate this monster.
Hiccup's father, the chief of the village (voice of Gerard Butler of 300), finds out about this and takes off to defeat it, little realizing that he and his men will be horribly outmatched. It's at this point that they had captured his son's dragon and are using it as a sort of compass to the location. Of course, Hiccup and his dragon come to the rescue at the end--and ultimately these Vikings and dragons establish a very different relationship.
This movie is far better than I thought it would be. While the dragons aren't the most realistic depictions of the creatures the style is interesting--and there's a wide variety of monsters, from small flying lizard-like ones, to two heads, to round pig-like scorchers with hummingbird wings. I would have loved to have seen this at the theater in 3-D, with all those flying scenes.