Lucid dreaming is the experience of becoming aware, while dreaming, that one is dreaming, and sometimes of gaining a measure of deliberate control over the content of the dream. Unlike most claimed out-of-body or visionary practices, lucid dreaming has been established as a genuine and studyable phenomenon by scientific research: in laboratory studies dreamers who became lucid were able to signal their awareness to researchers by prearranged patterns of eye movements while remaining asleep, confirming that a person can be consciously aware within a dream. The state has since been investigated as a window onto consciousness, sleep and the dreaming brain. Techniques for inducing lucidity, among them the habit of regularly questioning during waking life whether one is dreaming, and methods of returning to sleep with the intention of recognising the dream, have been developed and studied, and can increase the frequency of lucid dreams for many people.
Lucid dreaming has both a modern experimental and a long spiritual lineage. It has been cultivated for centuries within Tibetan Buddhism as "dream yoga," a practice in which the meditator learns to recognise and work within the dream state as a means of training awareness, loosening attachment to the apparent solidity of experience, and preparing for the transitions of death; the recognition that the dream is a dream is used as a step toward recognising the dreamlike, insubstantial nature of waking experience itself. In its modern secular form lucid dreaming is pursued for exploration, creativity, the confronting of nightmares, and simple wonder. It occupies an unusual place among the practices catalogued here in being at once a technique with genuine scientific validation and a discipline with a deep contemplative history, the two meeting on the common ground of trained awareness within sleep.