Scholars in the field of education have unanimously subscribed to the pivotal role of critical thinking in individuals' life in general and their academic life in particular (Bloom, 1956; Ennis, 2003; Dewey, 1933). The thrust of the current study was to investigate the extent to which the books employed for Teaching English as Foreign Language include critical thinking skills. To attain this goal, 3 series of English books, namely, Top notch, Interchange, and English files series utilized by language institutes in Iran were targeted. Next, a seventy two-item critical thinking checklist based on Likert-scale and consisting of twelve skills; namely, comprehension, application, analysis, synthesis, evaluation, deduction, induction, balanced-thinking, multiple perspective-taking, creative thinking, building community of thinkers, and knowledge was developed. The target skills on the checklist were mainly based on Bloom's taxonomy and the related literature on critical thinking. The checklist was validated by the researchers themselves and some experts in the field and the reliability coefficient was also estimated at 0.86. Then, two raters conducted a content analysis on the books and determined the magnitude of each skill. The data were analyzed through descriptive statistics and inferential statistics (Chi-square and Kruskal-Wallis Non-parametric tests). Findings of the study revealed that the books mainly tapped knowledge, comprehension, application and building community of thinkers skills and failed to acceptably include other skills reported to be of utmost importance for students' academic success. The comparison of the mean rank of the skills in the three books also disclosed that as for lower order thinking skills there wasn’t a significant difference among the books; however, as for other skills Top notch was marginally higher. The paper also discusses the lack of critical thinking in the classroom and materials and proposes some ways to include more critical thinking skills in the materials. The results of the study have significant implications for material developers, educational policy makers and teachers.