Corruption is extremely hard to measure because we are not always sure what we are measuring. (For more on measurement issues see Kaufmann et al. 2006; Sampford et al. 2006). Many people make judgements about how much corruption there might be, and often focus on a bad event or two to draw a judgement that corruption is rife. It is however important to try to measure corruption for two main reasons. First, it is an indicator of how well a society is performing in terms of a government's contract with its citizens. If there is bribery, extortion, misappropriation, self-dealing; if major capital and development projects serve an individual's financial interests rather than the public interest; if corporations bribe public officials to exploit natural resources; if human rights abuses are tolerated; if justice administration is inconsistent with the rule of law; then that society is more corrupt than those in which these behaviours are less or not part of the social fabric. Second, if we know how much corruption there is within a jurisdiction and the nature and quantity of those corrupt events, then remedial actions can be put in place and preventive measures can be implemented. Third, if we know if corruption is concentrated and how it is distributed, our prevention processes are enhanced.