The Purchasing Power Parity (PPP) puzzle is the challenge of reconciling the high short-term volatility of real exchange rates with the slow rate at which deviations from PPP dampen. PPP, first articulated by the Salamanca school in 16th-century Spain, posits that national price levels should be equal when converted to a common currency. While PPP is widely accepted as a long-run anchor for real exchange rates, empirical evidence shows that short-term deviations are large and volatile, with real exchange rate volatility comparable to nominal exchange rate volatility. Recent studies have found that real exchange rates tend toward PPP in the long run, but convergence is extremely slow, with deviations dampening at about 15% per year. This slow convergence is difficult to explain with nominal rigidities alone, as real shocks (such as changes in tastes or technology) can lead to slower adjustments. However, existing models based on real shocks cannot account for short-term exchange rate volatility. PPP is often tested using the law of one price, which states that similar goods should sell for similar prices across countries. Empirical evidence shows that this law is frequently violated, with significant price differentials even for similar goods. These differences are often attributed to nontraded goods, transportation costs, tariffs, and non-tariff barriers. Additionally, pricing to market, where firms charge different prices in different markets, can contribute to price disparities. The law of one price is also challenged by the fact that price differentials across countries are more volatile than within countries. This suggests that international goods markets are not yet as integrated as domestic markets. Studies have shown that the volatility of PPP deviations is much higher for similar goods across countries than for dissimilar goods within a country. Long-run convergence to PPP has been supported by studies using long-horizon data, showing that PPP deviations tend to dampen at a slow rate. However, the slow convergence is difficult to explain with traditional models, suggesting that other factors, such as real shocks and government spending, may play a role. The Balassa-Samuelson hypothesis, which suggests that rich countries have higher price levels due to productivity differences in traded and nontraded goods, is one such explanation. Overall, the PPP puzzle remains unresolved, with empirical evidence suggesting that international goods markets are not yet as integrated as domestic markets, and that short-term exchange rate volatility is driven by financial and monetary shocks, while long-term convergence is influenced by real factors.The Purchasing Power Parity (PPP) puzzle is the challenge of reconciling the high short-term volatility of real exchange rates with the slow rate at which deviations from PPP dampen. PPP, first articulated by the Salamanca school in 16th-century Spain, posits that national price levels should be equal when converted to a common currency. While PPP is widely accepted as a long-run anchor for real exchange rates, empirical evidence shows that short-term deviations are large and volatile, with real exchange rate volatility comparable to nominal exchange rate volatility. Recent studies have found that real exchange rates tend toward PPP in the long run, but convergence is extremely slow, with deviations dampening at about 15% per year. This slow convergence is difficult to explain with nominal rigidities alone, as real shocks (such as changes in tastes or technology) can lead to slower adjustments. However, existing models based on real shocks cannot account for short-term exchange rate volatility. PPP is often tested using the law of one price, which states that similar goods should sell for similar prices across countries. Empirical evidence shows that this law is frequently violated, with significant price differentials even for similar goods. These differences are often attributed to nontraded goods, transportation costs, tariffs, and non-tariff barriers. Additionally, pricing to market, where firms charge different prices in different markets, can contribute to price disparities. The law of one price is also challenged by the fact that price differentials across countries are more volatile than within countries. This suggests that international goods markets are not yet as integrated as domestic markets. Studies have shown that the volatility of PPP deviations is much higher for similar goods across countries than for dissimilar goods within a country. Long-run convergence to PPP has been supported by studies using long-horizon data, showing that PPP deviations tend to dampen at a slow rate. However, the slow convergence is difficult to explain with traditional models, suggesting that other factors, such as real shocks and government spending, may play a role. The Balassa-Samuelson hypothesis, which suggests that rich countries have higher price levels due to productivity differences in traded and nontraded goods, is one such explanation. Overall, the PPP puzzle remains unresolved, with empirical evidence suggesting that international goods markets are not yet as integrated as domestic markets, and that short-term exchange rate volatility is driven by financial and monetary shocks, while long-term convergence is influenced by real factors.