The Bible tells us a lot about the gift of tongues. Jesus says that it will be a sign of those who believe in Him, Peter and Paul describe it in the lives of new believers in the early church and Paul gives lots of good instruction in 1 Corinthians. It's even prophesied about in the Old Testament!
Jesus Christ tells us what to look out for in those who believe in Him:
And these signs will accompany those who believe: in my name, they will cast out demons; they will speak in new tongues. (Mark 16:17)
TONGUES IN THE EARLY CHURCH
In the book of Acts we read how the followers of Jesus are filled with the Spirit in the Upper Room at Pentecost:
When the day of Pentecost arrived, they were all together in one place. And suddenly there came from heaven a sound like a mighty rushing wind, and it filled the entire house where they were sitting. And divided tongues as of fire appeared to them and rested on each one of them.
And they were all filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance. Now there were dwelling in Jerusalem Jews, devout men from every nation under heaven…[ ]…And at this sound, the multitude came together, and they were bewildered because each one was hearing them speak in his own language…. [ ]
…Both Jews and proselytes, Cretans and Arabians—we hear them telling in our own tongues the mighty works of God. (Acts 2:1-47)
Later in Acts, in one of the most significant moments for the early church, Gentile believers are filled with the Spirit when Peter visits Caesarea:
While Peter was still saying these things, the Holy Spirit fell on all who heard the word. And the believers from among the circumcised who had come with Peter were amazed, because the gift of the Holy Spirit was poured out even on the Gentiles. For they were hearing them speaking in tongues and extolling God. Then Peter declared… (Acts 10:44-46)
Shortly after this experience, Peter tells the church leaders about what happened in Caesarea. He describes the Holy Spirit falling on the new converts, reporting, "As I began to speak, the Holy Spirit fell on them just as on us at the beginning." (Acts 11:15)
The Apostle Paul travelled to Ephesus as a missionary. He meets believers who have no knowledge of the Holy Spirit. He baptises them in the name of Jesus, lays hands of them and the Holy Spirit falls on them - the believers speak in tongues and prophesy:
While Apollos was at Corinth, Paul took the road through the interior and arrived at Ephesus. There he found some disciples and asked them, “Did you receive the Holy Spirit when you believed?” They answered, “No, we have not even heard that there is a Holy Spirit.” So Paul asked, “Then what baptism did you receive?” “John’s baptism,” they replied. Paul said, “John’s baptism was a baptism of repentance. He told the people to believe in the one coming after him, that is, in Jesus.” On hearing this, they were baptized in the name of the Lord Jesus. When Paul placed his hands on them, the Holy Spirit came on them, and they spoke in tongues and prophesied. There were about twelve men in all. (Acts 19:1-7)
THE GIFT OF TONGUES IN 1 CORINTHIANS
Paul writes the most about tongues in Scripture, especially in 1 Corinthians chapters 12-14. For example:
Now concerning spiritual gifts, brothers, I do not want you to be uninformed. You know that when you were pagans you were led astray to mute idols, however, you were led. Therefore I want you to understand that no one speaking in the Spirit of God ever says “Jesus is accursed!” and no one can say “Jesus is Lord” except in the Holy Spirit. Now there are varieties of gifts, but the same Spirit; and there are varieties of service, but the same Lord; (1 Corinthians 12:1)
Paul then lists the gifts of the Holy Spirit, including tongues and the interpretation of tongues:
For to one is given through the Spirit the utterance of wisdom, and to another, the utterance of knowledge according to the same Spirit, to another faith by the same Spirit, to another gifts of healing by the one Spirit, to another the working of miracles, to another prophecy, to another the ability to distinguish between spirits, to another various kinds of tongues, to another the interpretation of tongues. All these are empowered by one and the same Spirit, who apportions to each one individually as he wills. (1 Corinthians 12:8-11)
And God has appointed in the church first apostles, second prophets, third teachers, then miracles, then gifts of healing, helping, administrating, and various kinds of tongues. (1 Corinthians 12:28)
Throughout Chapter 13 of Corinthians, Paul continues to talk mention the gift of tongues:
If I speak in the tongues of men and of angels, but have not love, I am a noisy gong or a clanging cymbal. (1 Corinthians 13:1)
One day we will have no need for prophecy, tongues or knowledge:
Love never ends. As for prophecies, they will pass away; as for tongues, they will cease; as for knowledge, it will pass away. (1 Corinthians 13:8)
In Chapter 14, Paul instructs the church in Corinth to:
Pursue love, and earnestly desire the spiritual gifts, especially that you may prophesy. For one who speaks in a tongue speaks not to men but to God; for no one understands him, but he utters mysteries in the Spirit. On the other hand, the one who prophesies speaks to people for their upbuilding and encouragement and consolation. The one who speaks in a tongue builds up himself, but the one who prophesies builds up the church. Now I want you all to speak in tongues, but even more to prophesy. The one who prophesies is greater than the one who speaks in tongues, unless someone interprets, so that the church may be built up. …
...For if I pray in a tongue, my spirit prays but my mind is unfruitful. What am I to do? I will pray with my spirit, but I will pray with my mind also; I will sing praise with my spirit, but I will sing with my mind also.
...I thank God that I speak in tongues more than all of you...
....So, my brothers, earnestly desire to prophesy, and do not forbid speaking in tongues.
INTERCESSION IN THE SPIRIT
In Romans 8:26 Paul describes intercession in the Spirit:
Likewise, the Spirit helps us in our weakness. For we do not know what to pray for as we ought, but the Spirit himself intercedes for us with groanings too deep for words.
Jude 20 exhorts us to pray in the Spirit:
But you, beloved, building yourselves up in your most holy faith and praying in the Holy Spirit,
In Ephesians 6:18 Paul tells us to:
Praying at all times in the Spirit, with all prayer and supplication. To that end keep alert with all perseverance, making supplication for all the saints,
THE GIFT OF TONGUES PROPHESIED IN THE OLD TESTAMENT
Isaiah prophesies about the gift, hundreds of years before, in Isaiah 28:11-12:
For by people of strange lips and with a foreign tongue the Lord will speak to this people, to whom he has said, “This is rest; give rest to the weary, and this is repose”; yet they would not hear.
We know that Isaiah was referring to tongues because Paul quotes him in his first letter to the Corinthians:
In the Law it is written, “By people of strange tongues and by the lips of foreigners will I speak to this people, and even then they will not listen to me, says the Lord.” Thus tongues are a sign not for believers but for unbelievers, while prophecy is a sign not for unbelievers but for believers. (1 Corinthians 14:21-22)