The Curriculum Topic Study (CTS) process, funded by the National Science Foundation, helps teachers improve their practice by linking standards and research on how children learn mathematics to classroom practice. Keyed to the core book Mathematics Curriculum Topic Study, this resource helps mathematics professional development leaders and teacher educators understand the CTS approach and how to design, lead, and apply CTS in a variety of settings that support teachers as learners. By bringing CTS into schools and other professional development settings, mathematics leaders can enhance their teachers' knowledge of content, improve teaching practices, and have a positive impact on student learning.