|This article relies on references to primary sources. (March 2008)|
Kriyā (in Sanskrit "action, deed, effort") most commonly refers to a "completed action", technique or practice within a yoga discipline meant to achieve a specific result. Types of kriya may vary widely between different schools of yoga. Another meaning of Kriya is the outward physical manifestations of awakened kundalini. Kriyas can also be the spontaneous movements resulting from the awakening of Kundalini energy.
Kriya Shakti is "a power of thought" said to be greatly studied by yogis. Among the specific Kriya practices are: Kriya Yoga and other techniques. Kriya Yoga was revived by Mahavatar Babaji and various schools, including Paramahansa Yogananda's kriya yoga institute, Self Realization Fellowship, who claim to teach the original techniques.
The Hatha Yoga Pradipika describes the six kriya cleansing techniques. They should only be performed if there is an excess of fat or phlegm in the body.
Sudarshan Kriya 
Sudarshan Kriya is powerful rhythmic breathing technique that is said to work on mental, physical, and spiritual levels. Sudarshan Kriya is different from Kriya Yoga. This breathing technique was founded in 1982 by Sri Sri Ravi Shankar. Sudarshan Kriya is practiced by millions of people worldwide. It is found to be effective in improving well being(support immune system, detoxification, reduce stress) and peace of mind(reduce stress, relieve depression, improve creativity, enhance brain function). However, it may not be recommended in pregnancy and for people with certain Psychiatric disorders. Sudarshan Kriya is taught in various Art of Living courses.
Other techniques 
- Helena Petrona Blavatsky (1893 - 1897), The Secret Doctrine, London Theosophical Pub. House, 1893-97, ISBN 0-900588-74-8
- The Art of Living - Research
- Sudarshan Kriya, a stress buster - Times Of India
- How to Do Sudarshan Kriya