Mahaa Mrityunjaya Mantra is a Vaidik Mantra, appeared in Yajur Ved (TS 1.8.6.i  VS 3.60) addressed to Shiv the Tryambak (three-eyed). It appears in Rig Ved also - Mandal 7, Sookt 59, Mantra 12, Rishi Vashishth, Mantra Devtaa Rudra. Sometimes it is called "Mrit Sanjeevane Mantra". This is called the heart of Ved. Along with Gaayatree Mantra, it holds he highest place among the Mantra. It is called Rudra Mantra referring to Shiv's furious aspect. It is the highest Mantra along with Gaayatree Mantra.

Originally this Mantra was given by Shiv himself to Shukraachaarya after severe austerities - by hanging upside down from a tree for 20 long years - Vinshottaree Dashaa Period, with smoke blowing into him from a fire lit beneath. Even Brihaspati Jee was shocked at the prospect of such a terrible penance. Definition of Tapaswee Yog comes from this penance, as Shani Dev (Saturn) - punishment or hard toil; Ketu - as smoke blown into the nose and other forms of self-inflicting torture; and Shukra (Venus) must come together to define the personal ability of the Tapaswee.

Later it was handed over to Brihaspati through his son Kach; and then to Guru Vashishth Jee for the benefit of mankind.

The Mantra and Its Explanation
The Mantra and explanation was given by Shukraachaarya to Rishi Dadheechi when Dadheechi's body was cut and thrown by Raajaa Kshuv - the story as appeared in Shiv Puraan.Shukraachaarya Jee said - "O Dadheechi, I pray to Lord Shiv and give you the Upadesh of the highest Mahaa Mrityunjaya Mantra. The Mantra is in Anushtup Chhand and accordingly, is divided into four Pad composed of eight syllables each.

Om Tryambak Yajaamahe, Sugandhim Pushtivardhanam |
Urvaarukmiv Bandhanaan, mrityormuksheeya Maamritaat ||

Shukraachaarya said - "The first Pad is "Tryambakam Yajaamahe" and means - we worship or sing the praise of Lord Tryambak. Tryambak is the name of Lord Shiv as the father of the three worlds - Bhoo, Bhuvah and Swarg Lok. He is the father and the Lord of the three Mandal's - Soorya, Som and Agni Mandala. He is Maheshwar, the Lord of the three Gun's - Sattwa, Rajas and Tamas. He is the Sadaashiv, the teacher of the three Tattwa - Aatmaa Tattwa, Vidyaa Tattwa and Shiv Tattwa. He is the father (cause and source) of the three energies (Agni) - Aavaahaneeya, Garhapatya and Dakshinaagni. He is the father of all physical creation through the three Moorti Bhoot - Prithvi (solid), Jal (liquid) and Agni (Tejas or  energy). He is the Lord of the three Heavens created by the dominance of the three Gun - Rajas (Brahmaa), Satta (Vishnu) and Tamas (Shiv). Know Him to be the Nir-Aakaar (formless) Sadaashiv as He is above this physical mode and is their Maheshwar. This is the first foot of the Mantra (composed of eight syllables)."

The second Pad of the Mantra is "Sugandhim Pushtivardhanam". Sugandhim refers to the fragrance of the flower that spreads in all directions, and in a similar way Shiv is present in the entire creation, both animate and inanimate. In all the Bhoot (modes of existence), in the three Gun (nature of creation as being Sattwa, Rajas or Tamas), in the ten Indriyaan (five Gyaan Indriyaan or senses and five Karm Indriyaan or organs of action), in all the Dev (33 Devtaa are the source of all illumination and enlightenment) and the Gan (hosts of demi-gods), Shiv exists and pervades as the illumine Aatmaa (soul) and is their essence. Pushtivardhanam is now being explained. That inward dwelling spirit (Aatmaa), the Purush Shiv is the real sustainer of Prakriti (and not vice-versa as all people perceive). Starting with the Mahaa Tattwa (primordial state of matter/energy) to the individual parts of creation, the entire sustenance of the physically created beings (both animate and inanimate) is done by the imperishable Purush. You, I, Brahmaa, Vishnu, the Muni and even Indra and devtaa are maintained/ sustained (by the Aatmaa and that is Him). Since the Purush (Aatmaa - Shiv) is the granter of sustenance to prakriti (body/nature), he is 'Pushti-vardhanam'."

The next two Pad (consisting of sixteen syllables), "Urvaarukmiv Bandhanaan mrityormuksheeya Maamritaat" means - "Hey Prabhu! Just as the ripe cucumber is severed from the bondage of the creeper, in the same manner may we be delivered from death for the sake of immortality (Moksh). Rudra Dev is like Amrit (nectar of immortality). Those who worship Him with good Karm, penance and repentance, meditation, contemplation, prayer or praise, will surely renewed life and vigor. The strength of truth force (in this Mantra) is such that Lord Shiv shall definitely free the worshipper from the bondage of death because Shiv alone is the giver of bondage and Moksh.

This is the Mrit Sanjeevanee Mantra and has the power to give back life and rescue from death and great evils. You should adore Lord Shiv and recite this Mantra. Water sanctified with this Mantra should be drunk all the time. [Authors note: It is well known that the Rudraaksh bead is placed in a glass of water after being held in the palm during the recitation of the Mantra. This water is drunk during the day.]

Meaning of the Mantra
Aum, We worship the three-eyed Shiv, who is fragrant, who increasingly nourishes [his devotees]. By worshipping him, we may be liberated from death for immortality, just as the ripe cucumber easily separates itself from its binding stalk.

Aum is not spelt out in the Rig-Ved, but has to be added to the beginning of all Mantra as given in an earlier Mantra of the Rig Ved addressed to Ganapati. This Mantra is given in the prayer page of the Book "Maharishi Jaimini's Upadesa Sutra".

Mahaa Mrityunjaya Mantra and Maarkandeya Rishi
See the story of Maarkandeya Rishi