If you've read this book, it's pretty obvious what the title is all about. Walden is the name of the pond, just outside Concord, Massachusetts, where Thoreau lived alone for two years. Given that he's essentially writing an autobiography, he could have named his book Thoreau or Life and nobody would have batted an eye. So, why Walden?
Well, the pond is more than just a locale. It is, Thoreau frankly admits, a symbol, and a versatile one at that. (See "Pond in Winter," paragraph 6.) It represents both the inspiring beauty of untouched nature as well as man's capacity for a rich and spiritually fulfilling life, free from materialism. If he'd named the book Thoreau (or something of the sort), the focus would have been placed too much on man. As we know, Thoreau was all about nature. Originally published as Walden; or Life in the Woods, the revised 1862 title puts the novel's emphasis squarely on the pond, and thus, on nature itself.