The tradition of origin among Saint Thomas Christians relates to the arrival of Saint Thomas, one of the 12 disciples of Jesus at the ancient seaport Muziris on the Kerala coast in AD 52.^{[4][5][6][7][8]} The families Sankarapuri ,^[9] Pakalomattam, Kalli, and Kaliyankal were considered particularly preeminent, and historically the most aristocratic Syriac Christian families tended to claim descent from these families.^[10]

It is also possible for Aramaic-speaking Jews from Galilee to make a trip to Kerala in the 1st century. The Cochin Jews are known to have existed in Kerala around that time. The earliest known source connecting the apostle to India is the Acts of Thomas, likely written in the early 3rd century, perhaps in Edessa.

The text describes Thomas' adventures in bringing Christianity to India, a tradition later expanded upon in early Indian sources such as the "Thomma Parvam" ("Song of Thomas"). Generally he is described as arriving in or around Maliankara and founding Seven Churches and half churches, or Ezharapallikal: Kodungallur, Kollam, Niranam, Nilackal (Chayal), Kokkamangalam, Kottakkavu, Palayoor , Thiruvithamcode Arappalli and Aruvithura church (half church). A number of 3rd- and 4th-century Roman writers also mention Thomas' trip to India, including Ambrose of Milan, Gregory of Nazianzus, Jerome, and Ephrem the Syrian, while Eusebius of Caesarea records that his teacher Pantaenus visited a Christian community in India in the 2nd century. There came into existence a Christian community who were mainly merchants.

The 2011 Indian census found a total of 6,411,269 Christians in Kerala,^[1] with their various denominations as stated: Saint Thomas Christians (Syro-Malabar Church, Syro-Malankara Catholic Church, Malankara Orthodox Syrian Church, Jacobite Syrian Christian Church, CSI Syrian Christians, Mar Thoma Syrian Church, St. Thomas Evangelical Church of India, Chaldean Syrian Church and Malabar Independent Syrian Church) constituted 70.73% of the Christians of Kerala, followed by Latin Catholics at 13.3%, Pentecostals at 4.3%, CSI at 4.5%, Dalit Christians at 2.6% and other Protestant groups (such as Lutheran, Calvinist and other charismatic churches) at 5.9%.

The Saint Thomas Christians (Nasrani) of Kerala belongs to the churches which use the East Syriac Rite (Syro Malabar Church and Chaldean Syrian Church) and West Syriac Rite (Jacobite Syrian Christian Church, Malankara Orthodox Syrian Church, Mar Thoma Syrian Church, St. Thomas Evangelical Church of India, Syro-Malankara Catholic Church and the Malabar Independent Syrian Church). CSI Syrian Christians follow the Anglican rite. The Saint Thomas Christians form 70.73% of the Christians of Kerala and 12.5% of the total population of Kerala.^[11][12]

Around 61% of Christians in the state are Catholics which includes the Eastern Syrian Catholics (Syro Malabar Church and Syro Malankara Church) and the Latin Catholics of Kerala.^[13] The Oriental Orthodox Churches are Malankara Orthodox Syrian Church and Malankara Jacobite Syriac Orthodox Church. The Malankara Marthoma Syrian Church and St. Thomas Evangelical Church of India is an Oriental Protestant church. The Church of South India belong to the Anglican Communion. Major Pentecostal denominations in Kerala include the India Pentecostal Church of God, Assemblies of God in India, Church of God (Full Gospel) in India, and The Pentecostal Mission. There has been a strong presence of other Protestant groups in southern Kerala such as the Church of South India and The Salvation Army that are typically based on Anglican beliefs and trace their origins to British rule. They have a significant presence in Neyyattinkara taluk and Pathanamthitta district.

• St.Philomena's Forane Church, Koonammavu & St. Chavara Pilgrimage, Archdiocese of Verapoly, a Catholic Church in Koonammavu, Cochin.
• St. Mary's Orthodox Syrian Church, Niranam, Pathanamthitta- one of the oldest churches in India and founded by St. Thomas.
• St. Mary's Cathedral, Kundara, Kollam- contains a Holy Girdle believed to be dropped from the sky by the Virgin Mary to St. Thomas.
• St. George Orthodox Church, Puthuppally, Kottayam- commonly called the 'Puthuppally Valiyappally' and contains a shrine declared as the 'Georgian Pilgrim Centre of the East'. Relics of Saint George are also present at Puthuppally Pally.
• Our Lady of Dolours Basilica, Thrissur, Thrissur- commonly known as 'Puthanpally' ('new church') and the third-tallest church in Asia.
• St. Antony's Forane Church, Ollur, Thrissur- a well-known church, site of the famous 'Malakhayude Perunnal'.
• St. Peter and St.Paul's Church, Parumala, Pathanamthitta- important to Malankara Orthodox Christians as the burial site of St. Geevarghese Mar Gregorios.
• Basilica of St. George, Angamaly, Ernakulam- largest of its kind in India and the first church in Angamaly, which was formerly dedicated to St Mary. It was the seat of power of Syrian Christians till 16th century.
• St. Mary's Soonoro Cathedral Angamaly, built by Archdeacon George in 1567.
• Potta Ashram, Potta, Thrissur- a famous Catholic charismatic renewal centre in Kerala.
• St. George's Syro-Malabar Catholic Forane Church, Aruvithura, Kottayam- first church built in the Pala Eparchy and has a cross laid down by St. Thomas.
• St. Mary's Jacobite Syrian Cathedral, Manarcad, Kottayam- contains part of the Holy Girdle and was the site of the Jacobite ritual of the Holy Mooron in 1982 by the Patriarch of Antioch Ignatius Zakka I Iwas.
• Divine Retreat Centre, Muringoor, Thrissur- a famous retreat centre with a rehabilitation centre, retirement home and other centres.
• Orthodox Theological Seminary, Kottayam- first seminary in Kerala for the Malankara Church and currently owned by the Malankara Orthodox Syrian Church.
• St. Thomas Church, Malayattoor, Ernakulam- an international shrine and the site of St. Thomas' footprints and knee-prints, along with other historical sites.
• Manjinikkara Dayara, Omallur, Pathanamthitta- Syriac Orthodox monastery and contains the tombs of St. Ignatius Elias III and Mor Yulios Elias Qoro.
• St. George Church, Edappally, Ernakulam- foundation laid by Pope John Paul II and the site of the 'offering of fowls' during the Feast of St. George.
• St. Thomas Orthodox Cathedral, Kadampanad, Pathanamthitta- contains the tomb of Mar Thoma III and declared as a 'Marthoman Pilgrim Centre'.
• St. Peter and St. Paul's Church, Kolenchery, Ernakulam- contains the tomb of Mar Thoma VII and reopened recently for both Malankara Orthodox Christians and Jacobite Orthodox Christians.
• St. Thomas Church, Kothamangalam, Ernakulam- contains the tomb of St. Baselios Yeldo.
• St. Mary's Jacobite Church, Thamarachal, Ernakulam- pilgrim centre of St. Mary and famous for its 'Ettunombu'.
• St. George Orthodox Church, Chadanapally, Pathanamthitta- contained the relics of St. George for a while and site of the well-known 'Chembuduppu' annual ritual.
• St. George Orthodox Church, Cheppad, Alappuzha- contains the tomb of Mar Dionysius IV and a 600-year-old mural.
• St. Francis Church, Fort Kochi, Ernakulam- oldest European church and currently under control of the CSI.
• St. John Nepumsian's Forane Church Parappukkara, Thrissur- a rare pilgrim centre of St. John Nepumsian and contains a granite cross given by St. Francis Xavier.
• St. Joseph's Church, Mannanam, Kottayam- constructed by St. Kuriakose Elias Chavara and contains his tomb.
• Basilica of Our Lady of Ransom, Vallarpadam, Ernakulam- a National Pilgrim Centre and contains a privileged altar.
• St. Mary's Jacobite Syrian Church, Kattachira, Alappuzha- declared as a Global Marian Pilgrim Centre and contains an icon of St. Mary with tears of aromatic oil flowing from the eyes.
• Marth Mariam Forane Church, Arakuzha, Ernakulam- one of the oldest churches in Kerala and where Mar Varghese Payyappilly Palakkappilly served as a parish priest.
• Jerusalem Retreat Center, Thalore, Thrissur- a famous Catholic charismatic renewal centre in Kerala.

• Caste system among South Asian Christians
• Goan Catholics
• East Indian Catholics
• Mangalorean Catholics

• George K.M.,`Christianity in India Through the Centuries`,Authentic Books, Secunderabad,2007,2009.(ISBN 978-81-7362-786-6).
• Benedict Vadakkekara,`Origin of Christianity in India`,Media House, Delhi,2007.ISBN 81-7495-258-6.
• Agur C.M.,`Church History of Travancore`,Madras,1903 Reprint:Asian Educational Services, New Delhi,1990. (ISBN 81-206-0594-2).
• Visvanathan Susan,`The Christians of Kerala`,Oxford University Press, Delhi1993,1999.(ISBN 0195647998)
• George Menachery,`The St. Thomas Christian Encyclopaedia of India`,SARAS,Ed.Prof. George Menachery, Ollur,Vol.I 1982, Vol.II 1973, Vol. III 2009.
• George Menachery,`Indian Church History Classics`,SARAS,Ed.Prof. George Menachery, Ollur,Vol.I The Nazranies 1998.
• C. I. Issac, The Evolution of Christian Church in India, ISBN 978 81 7255 056 1 2014, Soorygatha Publishers, PB No 3517, Kochi 682 035