Practitioners perform Reiki most often in offices, hospitals, clinics, and private homes. The practitioner and client determine the number of sessions together. Typically, the practitioner delivers at least four sessions of 30 to 90 minutes each.

Practitioners use a technique similar to the laying on of hands, in which they claim to be channels for energy ("Ki") guided by a universal spirit or spiritual nature ("Rei") — flowing through their palms to heal a person wherever they may need healing. They also believe that if ki's flow is disrupted, the body's functioning becomes disrupted, and health problems can occur. The concept that sickness and disease arise from imbalances in a vital energy field is the foundation not only of Reiki but of some other CAM therapies, such as traditional Chinese medicine (in which the energy is called qi or chi) and homeopathy (vital force).

Reiki appears to be generally safe, and serious side effects have not been reported. Some practitioners advise caution about using Reiki in people with psychiatric problems.

Sometimes a Reiki client experiences what practitioners call a "cleansing crisis." The person may have symptoms such as a feeling of weakness or tiredness, a headache, or a stomach ache. Reiki practitioners believe that these are effects of the body releasing toxins. They advise the client on how to deal with such symptoms if they occur, such as by getting more rest, drinking plenty of water, or eating a lighter diet.