Long-run cross-country price data exhibit a puzzle. Today, richer countries exhibit higher price levels than poorer countries, a stylized fact usually attributed to the “Balassa-Samuelson” effect. But looking back fifty years, or more, this effect virtually disappears from the data. What is often assumed to be a universal property is actually quite specific to recent times. What might explain this historical pattern? We adopt a framework where goods are differentiated by tradability and productivity. A model with monopolistic competition, a continuum-of-goods, and endogenous tradability allows for theory and history to be consistent for a wide range of underlying productivity shocks.