TI's Corruption Perception Index was first launched in 1995 and it is one of the best-known instruments used by TI. It is a compound index, based on the data obtained from specialized surveys implemented by several independent renowned institutions. The index reflects the opinion of businesspeople and analysts all over the world, including experts in evaluated countries. Transparency International entrusts prof. Johann Graf Lambsdorff, residing in Passau, Germany with the calculation of the index.
The surveys used for the calculation of the CPI contain questions regarding the incorrect use of public function for personal gain, such as situations in which public officials take bribe in connection with public acquisitions, or situations in which public funds are dilapidated. Other questions verify the efficiency of anticorruption policies, which verifies political as well as administrative corruption.

TI requires a minimum of 3 sources so as to include a country in the CPI. The modification of the CPI coverage zone can be equally determined by the inclusion of a new source, or the elimination of an old one. Consequently, modifications of data sources determine the inclusion or exclusion of countries from the CPI; countries included may differ from year to year.
 The results of the CPI allow the classification of countries based on the levels of perception regarding corruption among public officials and politicians. The score obtained by each country is highly relevant for the level of perceived corruption; the position of individual countries in the classification varies each year, with the exclusion of old countries or the inclusion of new ones.

The Corruption Perception Index is calculated annualy and launched simultaneously by Transparency International headquarters and its national branches.