The present study aimed at exploring the causes and reasons of the EFL learners’ plagiarism. To this end, 150 females and males TEFL students from State and Azad universities in Iran, participated the study. A questionnaire developed by Rezanejad and Rezaeibased (2013) and a semi-structured interview which were piloted on a similar sample before administering were used as the instruments of the study. To triangulate the findings, for the qualitative part of the study, a semi-structured interview including 16 questions was run with 10 learners to collect the quantitative data at the end of the study. Based on the findings of this study, it was revealed that most of the students were aware of the concept of plagiarism and had the same definition of it. Moreover, their professors used the Internet and search engines to detect plagiarism and warned them about plagiarism continuously.  The students claimed inadequate information about how not to plagiarize and less command over English language to be the main reason of plagiarism. They heard of it from their university professors, then in workshops or seminars on plagiarism, and finally from their high school teachers. Moreover, they got familiar with the concept of plagiarism through university professors, friends or family members, newspapers and magazines, Internet, TV, and radio. The implications are discussed in terms of raising learners' awareness about plagiarism in EFL contexts.