Reference from Bhagavad Gita itself
Bhagavad Gita Chapter 4, Verse 1 declares: The Personality of Godhead, Lord Sri Krishna, said: I instructed this imperishable science of yoga to Sun God, Vivsvan. This is the first transmission of the knowledge of Bhagavad Gita from Lord Krishna to the Sun God.
The knowledge of Bhagavad Gita then was instructed by Vivsvan (i.e. Sun God) to Manu the father of mankind. The age of current Manu is calculated to last for 30.53 crores of years, of which only 12.04 crores have passed. It means Bhagavad Gita was spoken at least 12 crores of years ago. This is the second transmission of the knowledge of Bhagavad Gita from the Sun God to Manu
The knowledge of Bhagavad Gita was then instructed by Manu to Ikshvaku Maharaja. Maharaja Ikshvaku was a king of this planet earth in Tretayuga, which has 12 lakh years of duration. After that Dwaparyuga of 8 lakh years passed. After Dwaparyuga, Kali yuga completed just 5000 years so far. Thus, Bhagavad Gita was known to the human society for around 20 lakh years. This is the third transmission of the knowledge of Bhagavad Gita from Manu to Ikshvaku
Recent Transmission 5000 years ago
Since the originally spoken knowledge of Bhagavad Gita appeared to be obscure, Lord Krishna gave the same knowledge to Arjuna in the battle field of Kurukshetra 5000 years ago. This is the recent transmission. The day the knowledge of Bhagavad Gita was spoken is celebrated as Gita Jayanti.
Modern Era Preaching of Bhagavad Gita
Adi Shankaracharya (788 – 820) wrote an elaborate commentary on Bhagavad Gita. “Even a little study of Bhagavad Gita is sufficient to avoid meeting with Yamaraja in the hell”, Adi Shankaracharya proclaimed 1200 years before.
Bhagavad Gita Preaching 1000 Years Before
Sripada Ramanujacharya (1017 – 1137) wrote an elaborate commentary on Bhagavad Gita for the benefit of mankind in the mood of servitude to the Lord.
Bhagavad Gita Preaching 700 Years Before
Srila Madhvacharya (1238 – 1317) gave explanation to Bhagavad Gita and spread the Message of Godhead.
Bhagavad Gita Preaching 500 Years Before
Lord Chaitanya Mahaprabhu (1486 – 1533) predicted that the Name of Lord Krishna would spread in each town and village on the earth.
Bhagavad Gita Preaching in the last 50 Years
His Divine Grace A.C. Bhakti Vedanta Swami Prabhupada (1896-1977), the Founder Acharya of ISKCON, on the order of his spiritual master, spread the knowledge of Bhagavad Gita all over the world. His commentary of Bhagavad Gita which is celebrated as “Bhagavad Gita As It Is” has been translated into more than 70 languages around the world.