(Sanskrit: “Wheel of Time Tantra”), chief text of a divergent, syncretistic, and astrologically oriented school of Tantric Buddhism (Vajrayāna) that arose in northwestern India in the 10th century. The work represents the final phase of Tantric Buddhism in India, just prior to the Muslim invasion, but it has remained prominent in Tibet.

At the centre of the text's mandala (ritual drawing) is an image of the deity Kālacakra, another manifestation of the Buddha Akṣobhya, either alone or embracing his consort Viśvamātṛ (Mother of the Universe). Surrounding them are more than 250 divine figures, arranged in an outwardly radiating series of concentric circles and squares. Many of these are Hindu deities, and many of the ideas in the text suggest non-Buddhist and even non-Indian origins. The most notable innovation in this tantra is its astrological frame of reference. The figures constituting the mandala are identified with planets and stars, and the structure of the mandala—one of the most complex in Tantric Buddhism—is correlated with the temporal rhythms of the heavens.