Reiki, as aforementioned in earlier posts, is the first practice and modality that I learned. There are quite a few resources to turn to when seeking out this information: everything from books to the internet to person-to-person instruction. I, personally, find myself to be a traditionalist and believe the passing on of information is to be done teacher to student. Although reiki has taken on many forms to many people here you will find a brief history and description along with the benefits it bestows, from my understanding.
Reiki is an ancient, energetic healing modality that remerged in the late 19th century. Its origins are said to hail back to India and Tibet from a time much further away. As it is now, Reiki found its reemergence in Japan and so the name Rei, meaning Universal Life and Ki meaning energy are what we know it as today. Reiki is not a religion. If anything, reiki can be considered a spiritual experience and, in the time to come, will be known as more than a subtle science.
When a practitioner runs or channels reiki they use it to work with the body through energy centers called chakras. Chakra is translated to mean "wheel", "circle" or "point". Yes, every living being, including our wonderful planet, has energy centers within and without. These energy centers are as common and part of us as any receptors found within us cellularly and molecularly. The main chakras are located around major organs and systems of our bodies. Each chakra represents a different attribute of the human and when balanced allows the human to thrive optimally.
The important thing to remember is that because every living being has these energy centers, every living being has the ability to channel reiki. A great example of this would be a mother who may place her hands on or kiss a wound of her child; its instinctual, innate and an automatic intention for the mother to want to heal her child. The primary thing that sets a studied practitioner apart is the process of receiving the attunements. The best way I have described what these attunements provide is to liken an unattuned individual's energy channel with that of a pin hole. This is not to say that an unattuned individual literally has a channel that size but just to illustrate. Once attuned the individual receives an amplification or greater opening, allowing for a focused, higher level of energy to run through the channel. These attunements can only be passed on from a teacher to a student, a very sacred and traditional aspect of becoming a practitioner. This is why one can study and research as much as desired, independently, however, to garner the full benefit of the practice, studying with a master/teacher practitioner is always beneficial, especially if seeking that level of understanding and ability; there is much wisdom through experience that can be shared this way.
During a session, the practitioner channels Universal Life (rei) Energy (ki) to help balance and clear the energy centers of the body and works with the receiver's intention to heal and promotes an internal homeostasis that contributes to the process. I often call this the "faith" aspect of reiki. The receiver must be in that state of mind, ready to accept healing on all levels and surrender to the process regardless of what the outcome may be. It is important to note that the source of this energy is universal and seeded in love and therefore can do no harm, nor can the energy be directed for selfish intent. It is an intelligent energy and goes where it is needed. From a physical standpoint, the session is noninvasive and can be done sitting, lying down, with or without placing the hands on the body and even from a distance. The experience of session one has greatly depends on the practitioner and how they received their training along with what their guidance suggests.
Because this practice works with faith often a physical demonstration of this is required through exchange, there is a transactional nature or element to a session. In the past I have had those who ask, "why does one have to pay for reiki?" or "if you're doing this for good cause, why even charge for a session?" and the reason is really quite simple and it comes in the form of a question: does one truly appreciate what they have not worked for or have not placed a personal stake in? I like to illustrate this with the story of Mikao Usi's experience upon bringing reiki to the village once he rediscovered it all those years ago. He, being a man of good faith and character, started healing those around him willingly. He worked with the homeless and ailed and observed many great outcomes in doing so until he discovered that some of those who had healed ended up in the same conditions or worse within a given amount of time. These were those who had no stake in their healing, it was taken for granted and there was no gratitude for the gift. He realized that a transaction was required not only to show the intention of the seeker but to symbolize their desire to heal before God, the Divine and the Universe. This transactional aspect is different for every practitioner but usually comes in the form of a simple payment for the session.
Through past experience, I have been told that a reiki session is beneficial for the mind and emotions more so than for physical healing. That is not to say that the physical aspect of healing isn't present nor is that to say that something like a miraculous remission hasn't or won't take place. Often, I regard the physical aspect of healing as the great "side effect" of being mentally and emotionally balanced. Both of those aspects of the human intertwine so intricately with the physical aspect that most do not recognize physical ailments begin with these. Once the body has relief from the mental and emotional, the benefit is in that the mind and emotions are clear to work optimally on whatever ails the physical, the body, and this can happen both knowingly and unknowingly... Faith.