OM is perhaps the most well known of all mantras. In ancient India OM was refered to as the most subtle sound of all creation. That from which all arises.

"Om is composed of three letters, A, U, and M. These symbolize the practitioner's impure body, speech, and mind; they also symbolize the pure exalted body, speech, and mind of a Buddha.

Can impure body, speech, and mind be transformed into pure body, speech, and mind, or are they entirely separate? All Buddhas are cases of beings who were like ourselves and then in dependence on the path became enlightened; Buddhism does not assert that there is anyone who from the beginning is free from faults and possesses all good qualities. The development of pure body, speech, and mind comes from gradually leaving the impure states and their being transformed into the pure." His Holiness the Dalai Lama