This chapter deals with the recent development of Computational Thinking (CT) in the curricula of many countries, principally in mathematics. It aims at discussing, broadly, how CT changes the mathematical activity and impacts mathematical contents. More precisely, we study the relations between mathematics, computer science, mathematical thinking and computational thinking and discuss new content at the interface of computer science and mathematics as well as the transformation of mathematical content due to the integration of CT. We ground our discussions on examples of integration of CT and computer science in various countries, we further discuss the origins of CT in mathematics education, and offer an epistemological reflection on the disciplines of mathematics and computer science. Finally we discuss related issues for classroom implementation, teaching resources, and teacher development.