This paper provides a comparative study of mathematics textbooks as the primary construct via the Anthropological Theory of Didactics (ATD), which was founded by Yves Chevallard. The aim is to suggest principles that can be incorporated to improve the designing of mathematics textbooks. Definitions, examples, and tasks dealing with the teaching and learning of relations and functions, as sub-construct, from several mathematics textbooks in Norway and one textbook from Ethiopia was collected and analyzed using didactical tools such as types of representations, cognitive demand levels, and response types of mathematical tasks. In the findings, similarity and differences of textbooks, both within homogeneous and heterogeneous cultures, were adequately identified and explained in a way that the results contribute to the improvement of the intended curriculum. In doing so, it shows that ATD provides an excellent tool for textbook design research in the future.