<p>The purpose of this study was to develop mathematics textbooks based on High Order Thingking Skills (HOTS) for odd grade X students and improve the quality of teaching materials in terms of validity. This research is a development with a model of Analysis, Design, Development, Implementation, and Evaluation (ADDIE). The product of this research is HOTS-based mathematics textbooks. The results showed that this book has quality seen from several aspects, including the results of the assessment of textbooks by material experts showing criteria of valid or good (score 70.70), the results of assessment of teaching materials by media experts show criteria are very valid or very good (score 95.14), the results of the assessment of textbooks by linguists show very valid or very good criteria (score 89.58), and the results of assessment of textbooks by high school mathematics teachers show very valid or very good criteria (score 89.58).</p>