There are a large number of web sites and books on the subject of Reiki. Some of these are listed below:
Web Sites
What is REIKI
http://en.wikipedia.org/wiki/Reiki
REIKI
http://www.lifepositive.com/body/energy-healing/reiki/reiki.asp
About Pranic Healing
http://www.pranichealinghome.org/understand-healing.htm
Reiki, Questions & Answers
http://www.reiki.org/faq/questions&answers.html
Developing Your Reiki Practice
http://www.reiki.org/reikipractice/practicehomepage.html
How to Practice Reiki Self-Treatment
http://reikiinmedicine.org/daily-practice/how-to-practice-reiki-self-treatment/
Books
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Reiki for Beginners [Paperback] by David Vennells
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The Power of Reiki: An Ancient Hands-On Healing Technique [Paperback] by Tanmaya Honervogt
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The Original Reiki Handbook of Dr. Mikao Usui [Paperback] By Dr. Mikao Usui and Christine M. Grimm
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Reiki: The Healing Touch by William Lee Rand
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The Reiki Sourcebook, Revised and Expanded [Paperback] By Bronwen Stiene and Frans Stiene