Reiki is a simple, safe and natural Japanese holistic healing technique, a universal energy that can rejuvenate our body,  bring it back to balance. The word Reiki comes from the Japanese word Rei meaning universal / divine and ki (chi, prana) energy. That vital energy passes through our body, through the chakras and the meridians. It also runs around us through our energy field called Aura. It is actually a vital energy that keeps alive all living beings. It penetrates the entire space and gives life to all living creatures. 
Usui Shiki Ryoho - Usui is the founder, and Usui Shiki Ryoho means Usui natural healing system.
Ki energy can be activated for the purpose of healing. When we feel good and when we are healthy, energy flows without interference. The level of energy is high,we are healthy and disease-resistant, and we are dealing with life challenges more easily. If we are not happy, if we are in stress, tired and not resistant to disease, our level of energy is low. We struggle to deal with life and problems. Life energy is responsive to our thoughts and feelings. It is well known that negative thoughts are badly affecting our health. Reiki practitioner simply laid his hands on the person and Reiki energy will flow. The hands are laid in certain places and chakras, but it goes where it is needed. The client stays in clothes and can be in a sitting or lying position. The client can experience mental, emotional and spiritual changes. During treatment the client may feel warmth, tingling, relaxation of individual organs or the whole body. Reiki has no harmful side effects and after the first treatment clients feel better. They are relaxed and sleep better.
Reiki has brought positive changes into many people`s lives by bringing them inner satisfaction and balance, love, wisdom, harmony, well-being, spiritual progress, and a sense of peace. Reiki is called a holistic method because he heals the whole person - body, feelings, mind, and spirit. Reiki is safe and positive and can not hurt anybody.
Reiki is used in many hospitals in America and Canada, where many doctors and nurses are introduced to this method. Reiki is complementary to all kinds of therapies. So it will not undo the action of medicine or some medical therapies, it can only help them to work faster, better, and make the patient feel better.