Saṅghamittā (Saṅghamitrā in Sanskrit, nun's name Ayapali 282 BC – 203 BC) was an Indian Buddhist nun and believed to be the eldest daughter (Sri Lankan Tradition) of Emperor Ashoka (304 BC – 232 BC) from his first wife Queen Devi (302 BCE – 242 BCE). Together with her brother Mahinda, she entered an order of Buddhist monks. The two siblings later went to Sri Lanka to spread the teachings of Buddha at the request of Sri Lankan King Devanampiya Tissa (250 BC – 210 BC) who was a contemporary of Ashoka. Ashoka was initially reluctant to send his daughter (Sri Lankan Tradition) on an overseas mission. However, because of the insistence of Sangamitta herself, he finally agreed. She was sent to Sri Lanka together with several other nuns to start the nun-lineage of Bhikkhunis (a fully ordained female Buddhist monastic) at the request of King Tissa to ordain queen Anulā and other women of Tissa's court at Anuradhapura who desired to be ordained as nuns after Mahinda converted them to Buddhism.

After Sanghamittā’s contribution to the propagation of Buddhism in Sri Lanka and her establishing the Bhikkhunī Sangha or Meheini Sasna (Order of Nuns) there, her name became synonymous with "Buddhist Female Monastic Order of Theravāda Buddhism" that was established not only in Sri Lanka but also in Burma, China and Thailand, in particular. The day the most revered tree, the Bodhi tree, a sapling of which was brought by her to Sri Lanka and planted in Anuradhapura, and which still survives, is also celebrated every year on the Full Moon day of December as Uduvapa Poya or Uposatha Poya and Sanghamittā Day by Theravāda Buddhists in Sri Lanka.

Sanghamitra is known for the proselytisation activity among women that she pursued as her lifetime goal in Sri Lanka, along with her brother, Mahendra (called Mahinda in Sri Lanka) at the initiation of her father, Emperor Ashoka of the Maurya dynasty who ruled in India in the 3rd century BC. Ashoka, after adopting Buddhism, took to spreading tenets of Buddhism in nine other countries of the region. His contemporary in Sri Lanka, King Devanampiya Tissa, in close alliance with Ashoka, saw the arrival of Buddhism in Sri Lanka.

However, before deputing missions abroad in the region around India, Ashoka, in consultation with Venerable Moggaliputta Tissa convened a meeting of the Third Buddhist Council in which 1,000 Arahants participated. The purpose of this council meeting was not only to purge the Sangha of undesirable elements but also to take a view on the proselytisation of Buddhism. Moggaliputta presided over the Council meeting where it was decided to send nine delegations to different regions to spread Buddhism.

King Ashoka then sent out missionaries in nine different directions. The delegation that was sent south to Sri Lanka, at the request of Tissa, was led by Ashoka's son Mahendra. Before taking the long journey, Mahendra sought blessings of his mother. The delegation (considered a diplomatic mission) comprised six other Arhats, namely Ittiya, Uttiya, Sambala, Bhaddasala, young Samanera (nephew of Mahendra) and a Bhanduka (also a cousin of Mahendra). All members of the mission belonged to the royal family, indicating the importance Ashoka attached to spreading Buddhism in Sri Lanka.

This was also considered an opportune moment to spread Buddhism in Sri Lanka since Buddha himself had created awareness of his philosophy and precepts of Buddhism among the royalty and the common people during his three visits to Sri Lanka undertaken in the eight years following his enlightenment. Buddha, during his lifetime, had also created a social structure for the practice of Dhammavinaya or Dhamma (in Sanskrit: Dharma), which comprised the Sangha – order of bhikkhus (monks) and bhikkunis (nuns) to preserve his teachings for posterity. However, it was only King Tissa, realising the poor status of the religion in his country, desired fresh efforts by a delegation from India.

Mahendra arrived with his delegation at Anuradhapura where King Tissa, accompanied by his sister-in-law (brother's wife) Princess Anula with her entourage of 500 women, met him at the Mahamegha Garden. The Mahendra mission was very successful in introducing Buddhism to Sri Lanka. He established the Bhikkhu Order for men. However, thousands of women, starting with Anula, who had converted to Buddhism along with King Tissa, wished to be ordained into the Bhikkuni Order. Mahindra Thera expressed his inability to do so since this ordination had to be performed by a priestess or a Theri Arahat. He therefore advised the King to write to Emperor Ashoka and seek the services of his younger sister Theri Sangamitta, who was "profoundly learned", to be deputed to Sri Lanka for the purpose. He also desired that a sapling of the right branch of the Bodhi Tree (where the Tathagata got his enlightenment) from Bodh Gaya should also be brought by her to Sri Lanka. King Tissa then chose his Minister Prince Arittha (his nephew) for the purpose since the minister had volunteered to go to India on the condition that on his return he would also be ordained into the Bhikkhu Sasana by Thera Mahindra. This was agreed.

Sangamitta's parents were Emperor Ashoka and his first wife, Devi, who was a Buddhist. Her birth in 282 BC, as popularly known in published texts was as the second child of Ashoka and younger sister of brother Mahindra. She was born in Ujjeini (present day Ujjain in Madhya Pradesh in India). Her mother did not join Ashoka when he was crowned and her two children had embraced Buddhism. She was married at the age of 14 to Agribrahma, a nephew of Emperor Ashoka, who was also an Arhant. She had a son, Saamanera Sumana who also later became an Arhant and went along with his uncle Mahindra to Sri Lanka to preach Buddhism. Her teacher was Ayupala. She was ordained at the age of 18 into the Theravada Buddhism Order by their preceptor Dhammapala. Her brother was also ordained at the same time. With her dedicated perseverance to Dhamma she became an Arhant Theri and resided in Pataliputra (now known as Patna).