ZDM - Mathematics Education is one of the oldest mathematics education research journals. The papers appearing in the seven themed issues per year are strictly by invitation only followed by internal peer review by the guest-editors and external review by invited experts. The journal exists to survey, discuss and extend current research-based and theoretical perspectives as well as to create a forum for critical analyses of issues within mathematics education. The audience is pre-dominantly mathematics education researchers around the world interested in current developments in the field.