Informed by a multi-year field test funded by the National Science Foundation and by research studies designed to improve instruction and learning, the 4th Edition of Math Trailblazers is a significant revision of previous editions that is aligned with the Common Core State Standards of Mathematics. Goals of this revision included providing better and more explicit support for teachers, making the program components easier to use, and bringing Math Trailblazers up to date with the current research about how children learn mathematics. The curriculum is based on the view that students must solve problems and need proficiency with the basic skills to do so. Both concepts and procedures are important, and neglecting one will undermine the other. The result is a carefully balanced, focused, rigorous, and coherent program that excels in providing students with modeling and problem-solving experiences in meaningful, fun, and interesting contexts designed to help students develop the ability to think flexibly and strategically about mathematics.