Walden enjoyed some success upon its release, but still took five years to sell 2,000 copies. Despite its slow beginnings, later critics have praised it as an American classic that explores natural simplicity, harmony, and beauty. The American poet Robert Frost wrote of Thoreau, "In one book ... he surpasses everything we have had in America".
Critics were generally split over Thoreau's Walden. Scottish author Robert Louis Stevenson judged Thoreau’s endorsement of living alone in natural simplicity, apart from modern society, to be a mark of effeminacy, calling it "womanish solicitude; for there is something unmanly, something almost dastardly" about the lifestyle. Poet John Greenleaf Whittier criticized what he perceived as the message in Walden that man should lower himself to the level of a woodchuck and walk on four legs. He said: "Thoreau's Walden is a capital reading, but very wicked and heathenish... After all, for me, I prefer walking on two legs".
Today, Walden stands as one of America's most celebrated works of literature. John Updike wrote of Walden, "A century and a half after its publication, Walden has become such a totem of the back-to-nature, preservationist, anti-business, civil-disobedience mindset, and Thoreau so vivid a protester, so perfect a crank and hermit saint, that the book risks being as revered and unread as the Bible" The American psychologist B. F. Skinner wrote that he carried a copy of Walden with him in his youth, and eventually wrote Walden Two in 1945, a fictional utopia about 1,000 members who live together in a Thoreau-inspired community.