The Common Core standards released in 2010 for English language arts and mathematics have already been adopted by dozens of states. Just how much change do these new standards represent, and what is the nature of that change? In this article, the Common Core standards are compared with current state standards and assessments and with standards in top-performing countries, as well as with reports from a sample of teachers from across the country describing their own practices. (Contains 5 figures, 7 tables, and 2 notes.)