First, every healing practitioner in any field should follow a code of ethics. Reiki is no exception. Though Reiki is said to not be capable of harm, a practitioner can violate or harm a patient without physically hurting them. Most schools have their own rules and ethics that go along with the school. For this course I have paraphrased from a school called The International House Of Reiki which can be found online at www.reiki.net.au/copy.asp?id=AboutEthic

Respect all living beings.

Do Reiki with integrity, honestly, and responsibility.

Heal and teach your wisdom to your family, friends, and community as you spread Reiki throughout the world.

Treat all the people you heal with fairness and equality.

Always advise patients to try to heal themselves, if possible.

Do not make promises about Reiki's abilities because there are no guarantees in life.

Practitioners should never touch a patient's private parts, any wound, or any other part of the body which the patient does not want touched for any reason.

Do not gossip or reveal a patient's personal, private matters to anyone else.

Practitioners should not advise patients to do or not do anything outside their experience or practice; therefore you should not prescribe medication or tell patients not to take medication unless you are a doctor as well.

Reiki is not a substitute for emergency medical practices, but it could be used to help a situation.

These are all common sense guidelines, The last two are disclaimers.