The first part of the book treats the philosophy of mathematics. It contains both a critique of existing approaches, and a new philosophy of mathematics. For although the traditional paradigm is under attack, the novel and promising ideas in the Zeitgeist have not yet been synthesized. Social constructivism is offered to this vacuum. The second part explores the philosophy of mathematics education. It shows that many aspects of philosophical assumptions. By uncovering some of them, the aim is to put a critical tool into the hands of teachers and researchers.