We show that the price of a Treasury bond and an inflation-swapped TIPS issue exactly replicating the cash flows of the Treasury bond can differ by more than $20 per $100 notional. Treasury bonds are almost always overvalued relative to TIPS. Total TIPS–Treasury mispricing has exceeded $56 billion, representing nearly eight percent of the total amount of TIPS outstanding. TIPS–Treasury mispricing is strongly related to supply factors such as Treasury debt issuance and the availability of collateral in the financial markets, and is correlated with other types of fixed-income arbitrages, These results pose a major puzzle to classical asset pricing theory. In addition, they raise the issue of why the Treasury issues TIPS, since in so doing it both gives up a valuable fiscal hedging option and leaves large amounts of money on the table.