Corruption is what in the social sciences is known as an “essentially contested concept”. From the perspective of stating in empirical research of what constitute successful anti-corruption policies, this is certainly a problem. However, it should be underlined that the concept of corruption shares this problem with many, if not most, central concepts in the social sciences. To make this point, it should suffice to mention other central concepts like power, democracy, inequality, accountability, interest and representation, just to mention a few. Almost all things of interest in the world of social science are by definition “intangibles” since they mainly concern abstract principles or relations between agents and are therefore difficult to observe and measure.