Thomasine is a name given to a Syrian Christian group that originated in the first or the second century, who especially revered the apostle Thomas and some scholars speculate to have written the gospel of Thomas. They did not refer to their writing on the life of Jesus as an "εὐαγγέλιον" (euangélion); rather they seem to have preferred the word logia, meaning a book of sayings, as both the genre of their work which makes their approach different from the other early Christian authors. The group was said to have held esoteric, mystical, and ascetic ideas. Some have associated them with the Proto-Gnostics. However modern critics have disputed their affiliation with Gnosticism, especially because they lack many uniquely Gnostic beliefs.

According to one view the Thomasines were an early group that questioned the authority of the Jerusalem church and the apostle James, with the Thomasine church beginning around the middle of the first century in Syria.

Elaine Pagels dates the Thomasine community to around the time of the Gospel of John’s compilation (AD 70–110), and contends that the Gospel of John appears to contain "anti-Thomasine" elements and that the Johannine community may have splintered off from the same group, though there has been increasing skepticism of the existence of the Johannine community in the 21st century. Most scholars date Thomas to the second century, after the composition of the canonical gospels.

The Thomasine communities had leaders who through social rules, attempted to manage the process by which new proselytes could come in. They minimized the importance of money and were not expected to have any extra income from what they did not give away. The community had a social attitude of "diligence", where the leader of the community demonstrates a consistent structure for community activities, including labor. The Thomasines likely had a form of baptism.

In Thomasine belief, Jesus was referred to as "the Light" who ascended to the "place of light". Followers were encouraged to pursue a path toward said light through mystical ascent. The Thomasines identified themselves as "children of the light", contrasting this with those not part of the elect community, who were considered "sons of darkness". The Thomasines believed in predestination, viewing themselves as elect because they were born from the light.

The Gospel of Thomas says to keep the Sabbath to be saved. However, it is likely a metaphor for internalized rest. The Thomasines were also said to have had semi-ascetic ideas.

In Thomasine theology, the pursuit of light is associated with a journey that culminates in "rest." The choice to follow Jesus is considered significant, as judgment is perceived to be ongoing in the world, and there is a notion that the universe may conclude at any moment.

The Gospel of Thomas refers to Jesus as the "son of man" and affirms his lordship. For the Thomasines, Jesus is considered a figure whose nature resists simple categorization or description. However, certain passages in the Gospel of Thomas may suggest aspects of divine characteristics attributed to Jesus.