Competence with fractions is foundational to acquiring more advanced mathematical skills. However, achieving competency with fractions is challenging for many students, especially for those with mathematics learning difficulties who often lack foundational skill with whole numbers. Teaching fractions is also challenging for many teachers as they often experience gaps in their own fractions knowledge. In this article, the authors explain the sources of difficulty when learning and teaching fractions. Then, the authors describe effective instructional strategies for teaching fractions, derived from three randomized control trials. Implications for practice are discussed. [For the Grantee Submission to this article, see ED598359.]