The theory that, in the long run, identical products and services in different countries should cost the same in different countries. This is based on the belief that exchange rates will adjust to eliminate the arbitrage opportunity of buying a product or service in one country and selling it in another.  For example, consider a laptop computer that costs 1,500 Euros in Germany and an exchange rate of 2 Euros to 1 U.S. Dollar.  If the same laptop cost 1,000 dollars in the United States, U.S. consumers would buy the laptop in Germany.  If done on a large scale, the influx of U.S. dollars would drive up the price of the Euro, until it equalized at 1.5 Euros to 1 U.S. Dollar - the same ratio of the price of the laptop in Germany to the price of the laptop in the U.S.  The theory only applies to tradable goods, not to immobile goods or local services.  The theory also discounts several real world factors, such as transportation costs, tariffs and transaction costs.  It also assumes there are competitive markets for the goods and services in both countries.
Related information about purchasing power parity:
- Purchasing power parity - Wikipedia, the free encyclopedia
 Purchasing power parity (PPP) is an economic theory and a technique used to   determine the relative value of currencies, estimating the amount of adjustment ...
 
- Purchasing Power Parity (PPP) Definition | Investopedia
 Definition of 'Purchasing Power Parity - PPP'. An economic theory that estimates   the amount of adjustment needed on the exchange rate between countries in ...
 
- Purchasing Power Parity
 Purchasing power parity (PPP) is a theory which states that exchange rates   between currencies are in equilibrium when their purchasing power is the same   in ...
 
- A Beginner's Guide to Purchasing Power Parity Theory (PPP Theory)
 We'll take a look at the purchasing power parity theory (PPP theory) and show   what the theory implies. The Dictionary of Economics published by The   Economist ...
 
- What Is PPP or Purchasing Power Parity?
 Purchasing Power Parity (PPP) is an economic technique used to determine the   relative value of currencies. A common example of PPP...
 
- Purchasing Power Parity: Weights Matter - Back to Basics: Finance ...
 By Tim Callen - The rate at which the currency of one country would have to be   converted into that of another country to buy the same amount of goods and ...
 
- Purchasing power parity: Return of the Mac | The Economist
 Jun 8, 2012 ... FOR more than 25 years, The Economist has been producing Big Mac indexes.   At last, this burgernomics thing seems to be catching on.
 
- The Purchasing Power Parity Debate
 Purchasing power parity (PPP) is a disarmingly simple theory that holds that ...   the specific terminology of purchasing power parity was introduced in the years ...