Authentic materials are especially important for ESP trainees, since they reproduce an immersion environment and provide a realistic context for tasks that relate to learners' needs. Realia and authentic materials increase learners' motivation but are difficult to adapt to the learner's level of language, especially at the beginning level. It is also important to note that preparing such materials can be very time-consuming. Nowadays, authentic materials must be constantly updated, as they are more and more frequently on demand in ESP or EAP classes. A review of the different opinions of experienced authors and their arguments for and against the use of realia and authentic materials in the ESP classroom is offered in this article. A bibliography is included.