Generally unrecognized in his own day or, worse, dismissed as a second-rate imitator of his friend and mentor Ralph Waldo Emerson, Henry David Thoreau, in the twentieth century, has emerged as one of America's greatest literary figures. Walden, his account of two years spent living in a cabin on the shore of a pond in his native Concord, is universally recognized as the preeminent piece of American nature writing, though it is far more than simply a nature book. "Civil Disobedience," the account of and justification for his night spent in jail in Concord in protest against slavery, particularly through its influence on such activists as Mahatma Gandhi and Martin Luther King, has had wider political impact around the world than any other American literary document. As a prose stylist, Thoreau has been acknowledged by writers as disparate as Robert Louis Stevenson, Marcel Proust, Sinclair Lewis, and Henry...