Theosophy is a religious movement established in the United States in the late 19th century. Founded primarily by the Russian Helena Blavatsky and based largely on her writings, it draws heavily from both older European philosophies such as Neoplatonism and Indian religions such as Hinduism and Buddhism. Although many adherents maintain that Theosophy is not a religion, it is variably categorized by religious scholars as both a new religious movement and a form of occultism from within Western esotericism.

As presented by Blavatsky, Theosophy teaches that there is an ancient and secretive brotherhood of spiritual adepts known as the Masters, who are found around the world but primarily centered in Tibet. These Masters were alleged by Blavatsky to have cultivated great wisdom and supernatural powers, and Theosophists believe they initiated the modern Theosophical movement through disseminating their teachings via Blavatsky. Theosophists believe that these Masters are attempting to revive knowledge of an ancient religion once found around the world that will again come to eclipse existing world religions. Theosophy holds a monist position that there exists a single divine Absolute and articulates an emanationist cosmology in which the universe is perceived as outward reflections from this Absolute. The purpose of human life is spiritual emancipation and the human soul undergoes reincarnation upon bodily death according to a process of karma. Universal brotherhood and social improvement are guiding principles, although there is no particular ethical framework.

Theosophy was established in New York City in 1875 with the founding of the Theosophical Society by Blavatsky and Americans Henry Olcott and William Quan Judge. In the early 1880s, Blavatsky and Olcott relocated to India, where they established the Society's headquarters at Adyar, Tamil Nadu. Blavatsky described her ideas in two books, Isis Unveiled and The Secret Doctrine, which became key texts within Theosophy. Following her death in 1891, there was a schism in the Society, with Judge leading the Theosophical Society in America (TSA) to split from the international organization. Under Judge's successor Katherine Tingley, a Theosophical community named Lomaland was established in San Diego, California. At its height in 1895, there were 102 American branches with nearly 6,000 members. The Adyar-based Society was later taken over by Annie Besant, under whom it grew to its largest extent during the late 1920s, before going into decline after the Great Depression. TSA has since been reincorporated as a national section of the global Theosophical Society, which has a global membership of roughly 26,606 across 70 countries, including over 3,550 in the United States.

Theosophy played a significant role in bringing knowledge of Eastern religions to the West and encouraging cultural pride in South Asia. Many prominent artists and writers have also been influenced by Theosophical teachings. Theosophy has an international following, and during the 20th century had tens of thousands of adherents. Theosophical ideas have also inspired over 100 esoteric movements and philosophies, among them Anthroposophy, the Church Universal and Triumphant, and the New Age.

Helena Blavatsky, the founder of Theosophy, insisted that it was not a religion, although she did refer to it as the modern transmission of the "once-universal religion" that she said had existed deep into the human past. Theosophical organizations have maintained the belief that Theosophy should not be labeled a religion; instead, they regard it as a system that embraces what they see as the "essential truth" underlying religion, philosophy, and science. As a result, Theosophical groups allow their members to hold other religious allegiances, resulting in Theosophists who also identify as Christians, Buddhists, or Hindus.

Scholars of religion who have studied Theosophy have characterized it as a religion. In his history of the Theosophical movement, Bruce F. Campbell noted that Theosophy promoted "a religious world-view" using "explicitly religious terms" and that its central tenets are not unequivocal fact, but rather rely on belief. Olav Hammer and Mikael Rothstein termed it "one of the modern world's most important religious traditions". Various scholars have pointed to its eclectic nature; Joscelyn Godwin described it as a "universally eclectic religious movement", while scholar J. Jeffrey Franklin characterized Theosophy as a "hybrid religion" for its syncretic combination of elements from various other sources. More specifically, Theosophy has been categorized as a new religious movement. According to Maria Carlson, Theosophy is a "positivistic religion" "offering a seemingly logical theology based on pseudoscience."

Scholars have also classified Theosophy as a form of Western esotericism. Campbell for instance referred to it as "an esoteric religious tradition", while the historian Joy Dixon called it an "esoteric religion". More specifically, it is considered a form of occultism. Along with other groups such as the Hermetic Order of the Golden Dawn, the Theosophical Society has been seen as part of an "occult revival" that took place in Western countries during the late 19th century. The historian of religion Wouter Hanegraaff noted that Theosophy helped to establish the "essential foundations for much of twentieth-century esotericism". Although Theosophy draws upon Indian religious beliefs, the sociologist of religion Christopher Partridge observed that "Theosophy is fundamentally Western. That is to say, Theosophy is not Eastern thought in the West, but Western thought with an Eastern flavour."

At a meeting of the Miracle Club in New York City on 7 September 1875, Blavatsky, Olcott, and Judge agreed to establish an organisation, with Charles Sotheran suggesting that they call it the Theosophical Society. Prior to adopting the name "Theosophical", they had debated various potential names, among them the Egyptological Society, the Hermetic Society, and the Rosicrucian Society.