This dissertation investigates the utilization of authentic reading materials in ESL textbooks and the role that textbook-based tasks serve in enabling ESL classrooms to mirror the target environment. Three original studies are conducted, and two models are designed and applied in order to address the research questions, which aim to establish a standard metric for assessing semi-authenticity of materials and to determine to what degree ESL textbooks prepare students for utilizing subsequent academic textbooks in similar topical areas. Textbooks developed for ESL business and academic business courses are analyzed to determine task category prevalence, reading texts in the ESL genre undergo qualitative assessment on a material authenticity scale, and the source environments and thematic contexts of authentic reading materials are identified. Through the research explored and the studies performed, it is found that the model for continuum of authenticity scoring developed in this work is an effective technique to assess the authenticity of reading materials for comparison purposes. The studies conclude that authentic reading materials in ESL business textbooks are low in authenticity, that reading tasks are far less prevalent in ESL business textbooks than in academic business textbooks, and that the authentic reading materials in ESL business textbooks are sourced from authentic business environments and engage learners in the business-appropriate themes of business functions, cultures, and personalities. The findings demonstrate real challenges in preparing ESL students for academic environments considering the disparate utilization of content and engagement between the two textbook genres, which emphasizes the importance of teachers to supplement their classes with additional authentic materials beyond course textbooks. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]