This article reports on an educational design research study exploring the potential of combining entrepreneurship and mathematics – two of the key competencies stressed as important in a society of lifelong learning. The aim of the study was to explore what happens when entrepreneurship is integrated into mathematics lessons. Eight Swedish primary schools were involved in the iterative design wherein researchers and teachers together planned, implemented, and evaluated lessons. The results indicate that combining entrepreneurial and mathematical competencies may produce a win-win situation. Entrepreneurial competencies can be of value when students are learning mathematics, and at the same time mathematics teaching can be organised so that students develop both mathematical and entrepreneurial competencies.