This introduction starts by addressing why curriculum is a key concept in educational studies in mathematics. The general argument is that the curriculum concept makes it possible to connect processes of teaching and learning to wider societal structures. The more specific argument is that the curriculum concept enables studies of mass schooling, not least issues concerning change and governance, to be made. It is around this specific argument that this Handbook section and its chapters revolve. Thus, the second section of the introduction concerns the emergence of mass schooling and its connection to mathematics education, outlining also challenges related to change and governance. In the final section, the purpose and aims of the section are presented; and it then follows brief descriptions of each chapter’s content and how it is connected to the concepts of curriculum, mass schooling, change, and governance.