Astral projection
Astral projection (or astral travel) is a paranormal interpretation of an out-of-body experience achieved either awake or via lucid dreaming or deep meditation. The concept of astral projection assumes the existence of another body, separate from the physical body and capable of traveling to non-physical planes of existence. Commonly such planes are called astral, etheric, or spiritual.  Astral projection is often experienced as the spirit or astral body leaving the physical body to travel in the spirit world or astral plane.
Astral projection is controversial. Skeptics say that there is only the evidence of personal testimonials that anything actually leaves the body.

# Schools of thought
There are three general schools of thought on the nature of astral projection. These can broadly be defined as the separation model, the phasing model, and the skeptical model.

## Separation model
The separation model includes a large variety of belief systems, which say that astral projection takes place outside of the physical body. In this model, an astral or etheric body carries the consciousness outside of the physical body. Some, such as those who believe in Theosophy, say that the higher astral planes are reached through the progressive projection of subtler energy bodies from previous projected bodies, much like a Russian doll, while others believe in less complicated systems.  The subtle body is attached to the physical body by means of an energetic connection which usually takes the appearance of a silver cord 'plugging' into the chakra system.

## Phasing model
According to the phasing model, defined mainly by Robert Monroe, no "movement" actually occurs during astral projection.  The astral planes and the physical world are points on the spectrum of consciousness. When a person projects, they actually "phase" into another area of consciousness and the locales it contains. This can be likened to tuning a radio to another station.  The phasing model does not say that the mind is dependent on the brain, but only that our concepts of space do not necessarily apply to astral travel.

## Skeptical model
This model argues that astral projection is an experience which takes place in the mind/brain of the experiencer.  The exact mechanisms are unknown, but experiences somewhat similar to an Out-of-body experience -though without any experience of astral planes- can be induced with drugs or brain stimulation.

# Projection types or locations
The astral planes are usually conceived as either realms that overlap the physical in different layers, or as states of consciousness that need to be traversed in order.  Usually, the progression is from the physical to the etheric, then the astral, then various other realms or spirit worlds beyond the astral. 

## Astral projection
In astral projection the traveller finds him- or herself in an apparently real domain, which has no parallel to any physical setting.  This is termed by New Agers and occultists among others as the astral plane or "the astral". Environments here may range from populated to unpopulated, artificial to natural to completely abstract environments and from beautific to horrific. Here, normal physical laws often do not apply. The quality of detail ranges from crude to vivid and fascinating. Projectors may gain access to visions of the past or future of Earth, and to the Akashic records. It has been said that space and time do not exist on the astral plane in the same way they do on earth, or that they can be transcended.  Many travelers have theorized that people having dreams travel to the astral realms.  Travelers have reported seeing dreamers enact dream scenarios on the astral plane, unaware of the more extensive and varied non-physical environment surrounding them. Some also claim common movements in dreams, such as falling or feeling like you are walking through quicksand, is the astral body in action.
The astral environment is often divided into levels or planes.  There are many different views concerning the overall structure of the astral planes, and many different numbering schemes applied to them.  These planes may include heavens and hells, places where people go immediately after death, transcendent environments for those who are "more enlightened," and other less-easily characterized states.

## Etheric projection
Though closely related to astral projection, in etheric projection a projector encounters mainly that which exists physically, moving about in a (usually invisible) etheric body. The term was used as far back as the 1940s, by Dion Fortune in her book Psychic Self Defence.  In contrast to astral projection, during this type of experience, there are no fantastical worlds, or self-absorbed encounters; the majority of the experience can -hypothetically- be validated.
The world encountered during etheric projection may seem to be at variance with physical reality if strict mind control is not maintained. Robert Monroe describes this type of projection as a projection to "Locale I" or the "Here-Now", and describes it as containing people and places that actually exist in the material world.  Robert Bruce refers to a similar area as the "Real Time Zone" (RTZ) and describes it as the nonphysical dimension level closest to the physical.
In Western theosophy, each subtle body is functionally distinct. Since the etheric body and astral body are not the same, they cannot represent the same kind of psychic activity. 
According to Max Heindel, the etheric "double" serves as a medium between the astral and physical realms. Ether, also called prana, is the "vital force" that empowers the Physical forms in order for change to take place. This means that when one views the physical during an OBE, they are not technically "in" the astral realm at all.

# Research
Dr. Robert Crookall published case studies of astral projection in 1960. He divided these into naturally-occurring out-of-the-body experiences (people who nearly died, people who were very ill, people who were exhausted, etc, and people who were quite well) and enforced OBEs, from anaesthesia, suffocation, accidents and hypnosis.
Dr. Charles Tart tentatively concluded that etheric projection may have objective validity. For example, in a 1967 study, a subject was unable to discover a five digit number written down and placed face up in an adjoining room, but did provide some details of the activities of the technician monitoring the experiment. Tart summarizes, "Thus, there is some indication that ESP may have been involved with respect to the technician's activities, but it is not at all conclusive."
Robert Monroe, founder of the Monroe Institute, published several accounts of his experiences of astral projection, including Far Journeys. Monroe developed a method called "Hemi-Sync" to induce mental states that are favorable for projection. Hemisync is a method of altering brain waves using sounds, together with meditative instruction, listened to on headphones. The process is based on a concept called binaural beats.
Bruce Moen began as a student of  Robert Monroe, but has developed the process of mentally exploring through 'projection' in such a manner as to frequently override the need for sound wave support such as Hemi-Sync.