Extracted from the website of Buddhist Vajrayana Charity Funds Association and translated (遺教結集) into English:

Buddhist Councils on Legacy of Buddha’s Teachings

Buddhist Councils (samgīti; ketsujū結集), meaning group announcement, to gather together the general public, to announce the decision, and to be considered as the definitive version, is defined as ‘Buddhist Councils’. (Remark: Buddhist Councils were assemblies of monks held after Buddha Sakyamuni Nirvana to compile and confirm the Buddha’s teachings so as to ensure the accurate reservation and transmission.)
1.	The First Buddhist Council (about five hundred monks participated)
	Shortly after the Buddha’s Nirvana, Monk Su Batuo: “The benevolent (brothers), don’t worry. When the Buddha was alive, He often told us what we could do, what we couldn’t do, we were constantly trapped. Now we are free, we can do whatever we want.” Venerable Mahakasyapa, having heard such the unexpected words spoken by a monk, determined to establish the legacy of Buddha’s Teachings.
	Four months after the Buddha had passed away, Venerable Mahakasyapa selected five hundred monks, who were highly acclaimed both in academy and conduct. It took them seven months to complete the Buddhist Council, was called ‘Five Hundred Buddhist Council’. During this time, Venerable Mahakasyapa took the upper throne. Upali, the No.1 monk in upholding precepts, answered Venerable Mahakasyapa’s questions in establishing Vinaya (the precepts/monastic discipline) to be regarded as the Buddha System. This was followed by the highly receptive monk, Ananda, who announced the Buddha’s Dharma Teaching, to be regarded as the Buddha Speech.
2.	The Second Buddhist Council (about seven hundred monks participated)
	One hundred years after the Buddha passed away, in the town of Vaisali, a group of monks had a dispute over Vinaya (precepts/ monastic discipline). The Baqi monk group filled their copper bowls with water and invited the general public to throw money into it (consented to accept money), in return for auspiciousness. Yeshe elder, the disciple of Ananda, considered this as breaching Dharma.
	Thereafter, as the Baqi monk group generally had more people, it was called the General Public Division. The main stream faction comprised mostly of seniors, was called the Upper Throne Division.
	The Upper Throne Division gathered seven hundred people, recited Sutra, Vinaya and Sastra (Tri pitaka經律論三藏) repeatedly, and their prime consideration was the Vinaya (the precepts/ monastic discipline). This was the Second Buddhist Council, also known as ‘Seven Hundred Buddhist Council’.
3.	The Third Buddhist Council (Pataliputra Buddhist Council)
	Two hundred years after the Buddha passed away, within the grand temple built by Emperor Ashoka in the Peacock Dynasty, the monks were embroiled in disputes, and could not preach precepts in harmony for nine years. The Emperor ordered his attendants to warn the monks who failed to listen. The attendants killed the monks and disciples in anger. The Emperor was shocked when he heard this. He went to the temple to repent, not knowing who would be responsible for such wrongdoing.
	He then gathered sixty thousand monks, and chose Maudgaliputra Tisya (Pali: Moggaliputta Tissa) to chair the Buddhist Council. One thousand holy people, who were in the highest achievement in academy and conduct, were appointed to gather Sutra, Vinaya and Sastra (Tri pitaka經律論三藏). It was completed in nine months, in the town of Pataliputra, hence the Third Buddhist Council was also known as ‘Pataliputra Buddhist Council’.
4.	The Fourth Buddhist Council (The compilation set of Mahavibhasa)
	Five hundred years after the Buddha passed away, there was a famous Indian King, Kanishka (迦膩色迦王), who was a fervent believer of Buddhism. He felt that each division managed and preached differently. He then launched the Fourth Buddhist Council because of what Parsva(脅尊者) said.
	Kanishka chose five hundred holiest monks headed by Vasumitra (世友), with the objective of explaining Tri pitaka (三藏Sutra, Vinaya and Sastra).
	One hundred thousand verses《Upadeśa Sastra 鄔波第鑠論》was first established in explaining the Buddha Sutra. Then, one hundred thousand verses《Vinaya Vibhasa 毗奈耶毗婆娑論》was established in explaining the Vinaya. Finally, one hundred thousand verses《Abhidharma Mahavibhasa Sastra 阿毗達磨大毗婆娑論》was established in explaining the Sastra.
	Mahavibhasa widely explained the meaning. This Buddhist Council provided detailed explanation of the Sutra, Vinaya and Sastra; hence different from the First, Second and Third Buddhist Councils.