This volume focuses on research related to mathematics curriculum. But rather than focusing on results of research, it focuses on lessons learned about conducting research on curriculum, whether about design and development, analysis of curriculum in the form of official standards or textbook instantiations, teacher intentions related to curriculum implementation, or actual classroom enactment. For scholars interested in curriculum research, the volume offers lessons about conducting curriculum research that have been learned by others engaged in such work, including frameworks, tools, and techniques, as well as challenges and issues faced, with solutions to address them. Sharing lessons from authors of different countries strengthens the broader mathematics research community and provides insights that can help researchers make important strides forward in research on mathematics curriculum.