Learning English as a L2 has become a necessity for modern society because people use it as a communication tool all over the world. The mother tongue has been incorporated into teaching foreign/second languages from the early beginnings of language teaching. For this reason, it is of crucial importance to examine the amount of Croatian used in English second language classrooms. Additionally, the purposes of using the mother tongue in second language teaching can largely affect the whole process of learning a language. This thesis aims to investigate the amount of mother tongue usage and the purposes for its use in Croatian elementary school language classrooms, as well as Croatian teacher beliefs towards the L1 use. The method of investigation consisted of classroom observations in five elementary schools in Zadar and the administration of a teacher questionnaire to the five observed teachers. The classroom observations showed varied amounts of usage of the mother tongue among teachers. Moreover, Croatian English teachers mostly use the mother tongue in order to interact with learners, or for the purposes of giving running comments, repeating what the learners have already said, translating their own speech, and as arbitrary code-mixing. The results of the questionnaire proved that English language teachers had similar beliefs about the purposes for using Croatian in teaching English to eighth grade learners. However, it was also shown that most of the observed teachers may not be aware of how they actually incorporate the mother tongue into the lesson, that is, the specific purposes of mother tongue usage in the L2 classroom.