Transcendentalism is a philosophical, spiritual, and literary movement that developed in the late 1820s and 1830s in the New England region of the United States. A core belief is in the inherent goodness of people and nature, and while society and its institutions have corrupted the purity of the individual, people are at their best when truly "self-reliant" and independent. Transcendentalists saw divine experience inherent in the everyday. They thought of physical and spiritual phenomena as part of dynamic processes rather than as discrete entities.

Transcendentalism is one of the first philosophical currents that emerged in the United States; it is therefore a key early point in the history of American philosophy. Emphasizing subjective intuition over objective empiricism, its adherents believe that individuals are capable of generating completely original insights with little attention and deference to past transcendentalists. Its rise was a protest against the general state of intellectualism and spirituality at the time. The doctrine of the Unitarian church as taught at Harvard Divinity School was closely related.

Transcendentalism was thought to originally have emerged from "English and German Romanticism, the Biblical criticism of Johann Gottfried Herder and Friedrich Schleiermacher, the skepticism of David Hume", and the transcendental philosophy of Immanuel Kant and German idealism. Perry Miller and Arthur Versluis regard Emanuel Swedenborg and Jakob Böhme as pervasive influences on transcendentalism.

Transcendentalism is closely related to Unitarianism, a religious movement in Boston in the early nineteenth century. It started to develop after Unitarianism took hold at Harvard University, following the elections of Henry Ware as the Hollis Professor of Divinity in 1805 and of John Thornton Kirkland as President in 1810. Transcendentalism was not a rejection of Unitarianism; rather, it developed as an organic consequence of the Unitarian emphasis on free conscience and the value of intellectual reason. The transcendentalists were not content with the sobriety, mildness, and calm rationalism of Unitarianism. Instead, they wanted a more intense spiritual experience. Thus, transcendentalism was not born as a counter-movement to Unitarianism, but as a parallel movement to the very ideas introduced by the Unitarians.

Transcendentalism became a coherent movement and a sacred organization with the founding of the Transcendental Club in Cambridge, Massachusetts, on September 12, 1836, by prominent New England intellectuals, including George Putnam, Ralph Waldo Emerson, and Frederic Henry Hedge. Other members of the club included Sophia Ripley, Margaret Fuller, Elizabeth Peabody, Ellen Sturgis Hooper, Caroline Sturgis Tappan, Amos Bronson Alcott, Orestes Brownson, Theodore Parker, Henry David Thoreau, William Henry Channing, James Freeman Clarke, Christopher Pearse Cranch, Convers Francis, Sylvester Judd, Jones Very, and Charles Stearns Wheeler. From 1840, the group frequently published in their journal The Dial, along with other venues.

Sophia Peabody Hawthorne’s Cuba Journal is considered one of the earliest examples of transcendentalist writing shared among the Transcendental Club. The Cuba Journal predates Emerson’s Nature by two years and Thoreau’s Walden by more than a decade. Comprising 56 letters written during her stay in Cuba in the early 1830s, the journal is a richly descriptive account of the island’s landscape, flora, and atmosphere, focused on sensory experience and personal awakening. Though it avoided political or economic commentary, its celebration of nature’s beauty and spiritual resonance deeply influenced early Transcendentalist thinkers. Elizabeth Peabody, Sophia Peabody's sister, shared the letters widely, hosting reading parties—some lasting up to seven hours—where guests including Bronson and Abba Alcott, the Emersons, and the Channings took turns reading them aloud late into the night. Echoing themes that Emerson would later articulate, Sophia Peabody Hawthorne wrote: “[I]t is pure, single Nature, alone in her power & loveliness, that touches subdues and exalts the soul—We do not remember the godlike here—but we think of GOD here.”

By the late 1840s, Emerson believed that the movement was dying out, and even more so after the death of Margaret Fuller in 1850. "All that can be said", Emerson wrote, "is that she represents an interesting hour and group in American cultivation." There was, however, a second wave of transcendentalists later in the 19th century, including Moncure Conway, Octavius Brooks Frothingham, Samuel Longfellow and Franklin Benjamin Sanborn. The transcendence of the spirit, most often evoked by the poet's prosaic voice, is said to endow in the reader a sense of purpose. This is the underlying theme in the majority of transcendentalist essays and papers—all of which are centered on subjects which assert a love for individual expression. The group was mostly made up of struggling aesthetes, the wealthiest among them being Samuel Gray Ward, who, after a few contributions to The Dial, focused on his banking career.

Transcendentalists are strong believers in the power of the individual and are primarily concerned with personal freedom. Their beliefs are closely linked with those of the Romantics, but differ by an attempt to embrace or, at least, to not oppose the empiricism of science.