(from Greek glōssa, “tongue,” and lalia, “talking”), utterances approximating words and speech, usually produced during states of intense religious excitement. The vocal organs of the speaker are affected, the tongue moves without the conscious control of the speaker, and unintelligible speech pours forth. According to religious interpretations of the phenomenon, the speaker is considered to be possessed by a supernatural spirit, is in conversation with divine beings, or is the channel of a divine proclamation. Glossolalia occurred in some of the ancient Greek religions and in various primitive religions. There are references to ecstatic speech in the Hebrew Bible (1 Samuel 10:5–13, 19:18–24; 2 Samuel 6:13–17; 1 Kings 20:35–37), and in Christianity it has occurred periodically since the early years of the church.

Glossolalia first occurred among the followers of Jesus at Pentecost (Acts 2) when “they were all filled with the Holy Spirit and began to speak in other tongues, as the Spirit gave them utterance” (Acts 2:4). The apostle Paul (Paul, the Apostle, Saint) referred to it as a spiritual gift (1 Corinthians 12–14) and claimed that he possessed exceptional ability in that gift (1 Corinthians 14:18). The account in Acts (4:31, 8:14–17, 10:44–48, 11:15–17, 19:1–7) indicates that in the beginning of the Christian church the phenomenon reappeared wherever conversion and commitment to Christianity occurred. Paul urged restraint in the practice, however, since such a spectacular spiritual gift could be abused. Edification, as opposed to personal satisfaction, was set as the test of acceptable glossolalia.

The greatest emphasis upon the gift in the early church was made by followers of the 2nd-century prophet Montanus. His excommunication about 177 and the later decline of the sect probably contributed to a climate of opinion unfavourable to speaking in tongues, and the practice declined.

During later church history, glossolalia occurred in various groups. In modern times, it occurred during various Protestant revivals in the United States in the late 19th and early 20th centuries. These revivals resulted in the establishment of many Pentecostal churches, which in the late 20th century had more than 8,000,000 members. During the 20th century speaking in tongues also occurred occasionally in some of the older Christian churches, including the Roman Catholic, Anglican, and Lutheran churches.

In addition to the religious interpretations of glossolalia as a supernatural occurrence, various psychological interpretations have attempted to explain it as a natural occurrence, most commonly a hypnotic phenomenon resulting from religious excitement.