Congress recently created a new national observance, Constitution Day, to be marked each year on September 17th. This observance presents a valuable opportunity for the vastly diverse American populace to celebrate its shared values. But what, exactly, should Americans celebrate about the Constitution? The Constitution’s text is hardly perfect, and judicial interpretations of the Constitution are themselves problematic. To identify what Americans should celebrate on Constitution Day, this article sets out to identify the Constitution’s core meaning for Americans. To do so, it first draws lessons from two contemporary Establishment Clause disputes (one over the teaching of intelligent design and the other over the public display of Ten Commandments monuments). These disputes help illustrate why a secular Constitution and not a non-sectarian faith in God is the best source of shared values for Americans. The article concludes that the Constitution is important not so much for what it says but for what it symbolizes for Americans. It is a symbol of our secular society’s commitment to the dignity and humanity of every individual. This commitment and the values it entails refute the claim that our society will be valueless unless grounded upon religious belief.