Atirudra Maha Yaga as the name suggests is a Yaga which would be performed for 11 long days for "Goodness of humanity". The word Rudra means "Fire coming from the bowels of Earth spreading God's grace all over the world". This great Maha Rudra Yaga is performed by a very large number of priests in sannidhi/presence of Lord Shiva. The Yaga should be performed for a minimum of 11 days, in other words , 10 or less days is never permitted. The number 11 in this Yaga has a special significance in Srirudra. Srirudra Patam contains 11 Anuvakas.
After the completion of one round chanting on Rudra, one Anuvaka would be completed. 11 of those Anuvaka leads to Chamakam. 11 recitation of Rudra, followed by one recitation of Chamaka sums up to what is called "Ekadasha Rudra". This is one integral part of the Homa. 11 such rounds of the Ekadasha Rudra leads to "Laghu Rudra". 11 Laghu Rudra chanting is 1 "Maha Rudra" and 11 Maha Rudra recitation is one "Ati Rudra".
In the process of Yaga, certain rules has to followed. Prominent among them being that everyday one Maha Rudra should be completed. So a 11 day Yaga certainly would lead to a Atirudra. So on completion of one Atirudra, there would have been 14,641 Srirudra chanted by 121 Rutwiks across 11 days with 1331 Rudra Homas performed simultaneously in 11 Homa Kundas.
This entire program will be accomplished by chanting of Rudra by 140 learned priests for 14641 times and recitation of Rudra Anuvaka for 21,43,58,881 times. The biggest plus point of this Yaga is the fact that major portion of all 4 vedas(Rig, Yajur, Sama, Atharva) will be recited all the 12 days and is not found in any other Yaga of its kind. This Yaga was once performed by Lord Shiva himsef after Slaying of the demon Bhasmasura. This Yaga is always performed under the leadership of a KARTA (or performer). Rudra Abhisheka and other rituals would be performed everyday and Rudra Homas take place in Homa Kundas raised all over the performing area. Gayathri Homas would be carried out every morning and afternoon. Before the commencement of Yaga, a number of poojas, japas and havanas would be carried out, Maha Ganapathi Homa being prominent among them. Vasoddhara Homa is also performed everyday at near end signifying the end of days Yaga.
Rudra Abhisheka, Ekadasha Rudra Abhisheka, Maha Rudra Abhisheka and Athi Rudra Abhisheka are the 4 types of Abhishekas as said by the Sage Satapatha wherein the preceding one is more powerful than the earlier one. This AthiRudra Yaga is often said as "The Sigle most Wonderful and Divine Yaga of all time" and one should be blessed to witness a Athi Rudra Yaga in his/her life.