The Common Core State Standards (CCSS) for K-12 English language arts/literacy and mathematics, released in 2010, have been adopted by 49 states and territories; the District of Columbia; and the U.S. Department of Defense schools, which serve the children of U.S. service members around the world. The widespread adoption of the CCSS is a major step forward, yet significant work remains for states to successfully implement the new more rigorous and relevant academic standards--notably, the adoption of new tests to measure students' progress against the CCSS. This paper reports on states' challenges and progress in creating and launching assessments of students' learning that are aligned with the CCSS.