One prominent feature of many ESP (English for Specific Purposes) courses, which make them rather different from EGP (English for General Purposes) courses, is the presence of adult learners, who are primary workers and secondary learners. As ESP is a highly learner-cantered approach, paying close attention to the multidimensional needs of learners is of essential importance. Therefore, ESP teachers should follow a comprehensive adulthood-oriented approach, not only focusing on the linguistic needs of learners but also paying particular stress on the learners' psychological needs and preferences. In this humanistic context, an ESP teacher should follow an integrative approach, acting as a simultaneous teacher and counselor. Thus, ESP teachers should go beyond classroom settings, which lead them to their second important role concerned with a close collaboration with content teachers. This collaboration provides ESP teachers with useful information on the most effective syllabuses and instructional approaches to meet the learners' needs. Unfortunately, due to the unreasonable prejudice of many content teachers, it is rather difficult for many English teachers to develop a close collaboration with them. In response to this difficult situation, cooperation between English teachers and ESP learners is highly recommended. ESP teachers should also act as action-based researchers and theorizers to fulfill the ongoing needs of language learners effectively.