Ah, I still remember the first time I read this one, back when I was twelve or so -- it and The Lord of the Rings in one frantic weekend. It was a good weekend.
Lost count of how many times I've read it since, though it's no longer the all-consuming reading marathon. But still a delight, even if an imp was comparing it to the other Middle Earth works -- Middle Earth not being entirely consistent.
Bilbo Baggins, a contended, well-to-do hobbit, is sitting on his threshold, smoking and blowing smoke rings, when the wizard Gandalf comes by. And after a brisk conversation, Bilbo ends up inviting him for tea. Which he comes to with thirteen dwarves. And between one thing and another, Bilbo finds himself swept off on their quest for their mountain, where the dragon Smaug still hoards their gold from years ago. He's in over his head as they troop merrily off to face trolls, and goblins, but when he faces worse things, at the roots of the mountains, he slowly learns to hold his own. Until the climax where he features as trying an unusual way to bring things about.