Purchasing Power Parity (PPP) is claimed to be the oldest and simplest theory in determining the exchange rates of currencies. With its three versions, absolute PPP, relative PPP, and efficient markets PPP, this theory argues that price index levels of the countries are considered while setting the exchange rates. In this study, a general review of the theorj' and its failures are initially summarized. As the main purpose of the paper, the relative PPP has been applied for Turkey between 1980 and 1987 by taking USA as the comparision country. The application has been concentrated on both the official and black-market exchange rate determinations.