The article analyses the expression “to speak in [other] tongues” (λαλεῖν [ἑτέραις] γλώσσαις) as used in the Acts of the Apostles 2:4, 11; 10:46; 19:6. The author places special emphasis on the interpretation of the text from Acts 2:4, which, traditional biblical exegesis treats on a par with the text from Acts 2:6, 8, 11 because of the adjective ἑτέραις. In the author’s opinion, λαλεῖν ἑτέραις γλώσσαις from Acts 2:4 is to be understood as “speaking in languages that are different from the speaker’s own language and not understood by either the speaker or the listener without prior learning” (glossolalia) rather than in the meaning of speaking in a foreign language understood by the listeners but not understood by the speaker without prior learning (xenoglossy). This inference is derived from the lack of the definite article in Acts 2:4 before the word γλώσσαις and the lack of the basic language function, which is the communication between the speaker and the listener. The author believes that the descent of the Holy Spirit described in Acts 10:44–48 and 19:2–7 is identical with the experience of 120 people gathered in the Upper Room on the Day of Pentecost (Acts 2:1–4). These three Lucan passages describe the phenomenon of glossolalia; only Acts 2:6, 8, 11 is an account of xenoglossy.