On July 15-17, 2012 the United States National Commission on Mathematics Instruction and Seoul National University held a joint Korea-U.S. workshop on Mathematics Teaching and Curriculum. The workshop was organized to address questions and issues related to math teaching and curriculum that were generated by each country, including the following: What are the main concerns in the development of the curriculum? What issues have been discussed or debated among curriculum developers, teachers, teacher educators, and scholars regarding the curriculum? How have textbooks been developed for the curriculum? How are curricular tasks designed and what criteria are used? What is the role of learning trajectories in the development of curriculum? This report summarizes the presentations and discussions at the workshop.