The important question of who should teach English for Specific Purposes (ESP) courses has been a controversial issue for long. The present study aimed at exploring 300 ESP university students' points of view, 60 English as a Foreign Language (EFL) and field specialist ESP teachers' perceptions towards the most entitled agents to deliver ESP courses in Iran: field specialists or EFL teachers. To this end, the opinions of the participants who were sampled from three key Iranian universities were investigated through questionnaires and interviews. The results of the questionnaire revealed that there is not a significant difference in the perceptions of ESP students regarding the advantage of one group of teachers (field specialists or EFL teachers) over the other on teaching ESP courses, but they asserted that EFL teachers could be the right teachers for ESP instruction providing that they receive prior training. Furthermore, the results of the interviews from the two groups of teachers indicated that both language and field specialists preferred ESP courses to be collaboratively taught by both EFL and field specialist teachers in order to improve the students' knowledge and motivation for learning. Findings have implications for policymakers and teachers of ESP.