Walden (first published as Walden; or, Life in the Woods) is an American book written by noted transcendentalist Henry David Thoreau. The work is part personal declaration of independence, social experiment, voyage of spiritual discovery, satire, and manual for self-reliance. First published in 1854, it details Thoreau's experiences over the course of two years, two months, and two days in a cabin he built near Walden Pond, amidst woodland owned by his friend and mentor Ralph Waldo Emerson, near Concord, Massachusetts. The book compresses the time into a single calendar year and uses passages of four seasons to symbolize human development.

By immersing himself in nature, Thoreau hoped to gain a more objective understanding of society through personal introspection. Simple living and self-sufficiency were Thoreau's other goals, and the whole project was inspired by transcendentalist philosophy, a central theme of the American Romantic Period. As Thoreau made clear in his book, his cabin was not in wilderness but at the edge of town, about two miles (3 km) from his family home.

I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived. I did not wish to live what was not life, living is so dear; nor did I wish to practice resignation, unless it was quite necessary. I wanted to live deep and suck out all the marrow of life, to live so sturdily and Spartan-like as to put to rout all that was not life, to cut a broad swath and shave close, to drive life into a corner, and reduce it to its lowest terms, and, if it proved to be mean, why then to get the whole and genuine meanness of it, and publish its meanness to the world; or if it were sublime, to know it by experience, and be able to give a true account of it in my next excursion.