Nowadays, digital tools for mathematics education have become sophisticated and widely available. These tools offer important opportunities, but also come with constraints. Some tools are hard to tailor by teachers, educational designers and researchers; their functionality has to be taken for granted. Other tools offer a myriad of possible educational applications, which requires didactical choices to be made. In both cases, one may experience a tension between a teacher’s didactical goals and the tool’s affordances. From the perspective of Realistic Mathematics Education, this challenge concerns both guided reinvention and didactical phenomenology. In this chapter, this dialectic relationship will be addressed through the description of two particular cases of using digital tools in Dutch mathematics education: the introduction of the graphing calculator, and the evolution of the online Digital Mathematics Environment. From these two case descriptions, it is concluded that students need to develop new techniques for using digital tools; techniques that interact with conceptual understanding. For teachers, it is important to be able to tailor the digital tool to their didactical intensions. From the perspective of Realistic Mathematics Education, we conclude that its match with using digital technology is not self-evident. Guided reinvention may be challenged by the ridged character of the tools, and the phenomena that form the point of departure of the learning of mathematics may change in a technology-rich classroom.