Kriya - Yoga is based on Raja Yoga and has his fundament in the Katha - Upanishad. Patanjali points on Kriya-Yoga in his Yoga-Sutras.
The modern Kriya - Yoga comes from Lahiri Mahasya from southindia. It was spread in the west since the beginning of the last century through Yoganada, who had been sent by his guru Babaji.
Babaji became famous in Yoganandas book "Autobiography of a Yogi". Meanwhile a cult has developed around the four founders of this direction of Kriya-Yoga.
Kriya-Yoga is a very effective spiritual path, but without a special hint on introspection. The promises about leadership and protection of the gurus are the usual empty promises just like in other organizations.
The contents aof the teaching-letters are a bit too much for simple people of the american westcoast 100 years ago. Exercises for beginners are :
* The AUM(OM)-Technique is pure and excellent Nada-Yoga.
* The Hong-Sau-technique opens to the inner light.
Later an additional concentration-technique with a long mantram is given to the initiated disciple together mit further techniques.
These yoga-exercises belong to the best methods on the spiritual market. In the USA Guru Yogananda founded the SRF, which later had several unwanted branches, together with the Ashram in southindia.
These scools should not be mixed up with the scool of the late Guru Babaji from Histanapur in the Himalaya.