Glossolalia or speaking in tongues is the fluid vocalizing (or less commonly the writing) of speech-like syllables that lack any readily comprehended meaning, in some cases as part of religious practice. The significance of glossolalia has varied in context, with some adherents considering it as a part of a sacred language. It is most prominently practised within Pentecostal and Charismatic Christianity but it is also practised in non-Christian religions.
Glossolalia also sometimes refers to xenoglossy, the putative speaking of a natural language previously unknown to the speaker. 20th century Pentecostalism was not the earliest instance of "speaking in tongues" in church history, but earlier examples are few; in church history and writing after the New Testament, it had never been regarded as orthodox until the rise of Pentecostalism.
References to speaking in tongues by the Church fathers are rare. Except for Irenaeus' 2nd-century reference to many in the church speaking all kinds of languages "through the Spirit", and Tertullian's reference in 207 AD to the spiritual gift of interpretation of tongues being encountered in his day, there are no other known first-hand accounts of glossolalia, and very few second-hand accounts among their writings.
What we do have are general remarks that Christ had given the gifts of the Spirit to the church, and that the gifts in general remained in the church.