In mathematics education, textbooks are a main resource for daily teaching practice. Therefore, textbooks have a major impact on the learning opportunities offered to students. The aim of this PhD study was to get a better understanding of Dutch primary school mathematics textbooks regarding their contribution to the opportunity to learn. To this end, textbooks based on different didactical approaches and published in different time periods were studied on three features: the included learning content, the articulated performance expectations, and the incorporated learning facilitators. The research revealed that textbooks differ greatly in the learning opportunities they provide to students. These differences were found to be related to the textbook’s didactical approach. The textbooks appeared not only to vary in the learning facilitators they provide – which could be expected when the didactical approach differs – but also in the content and performance expectations. Furthermore, it was found that textbooks differ in their alignment with the formally intended curriculum in the Netherlands. An important consequence of the difference in learning opportunities is that not all students are exposed to the same content and performance expectations. This is even the case when students are taught with the same textbook, because due to the organizational structure of textbooks, not all students are presented all parts of them. Regarding the Dutch approach called Realistic Mathematics Education, textbook analysis revealed that this reform, when it started in the late 1960s, had already early precursors. Also, it was found that Realistic Mathematics Education over the course of the fifty years that it now exists, was and still is, clearly present in textbooks. Yet, textbook analysis showed that certain learning facilitators, presented in most or all textbooks, deviate from the original intentions of this reform.