Forms of corruption vary, but include bribery, extortion, cronyism, nepotism, patronage, graft, and embezzlement. Corruption may facilitate criminal enterprise such as drug trafficking, money laundering, and human trafficking, though is not restricted to these activities. Misuse of government power for other purposes, such as repression of political opponents and general police brutality, is not considered political corruption. Neither are illegal acts by private persons or corporations not directly involved with the government.

The activities that constitute illegal corruption differ depending on the country or jurisdiction. For instance, some political funding practices that are legal in one place may be illegal in another. In some cases, government officials have broad or ill-defined powers, which make it difficult to distinguish between legal and illegal actions. Worldwide, bribery alone is estimated to involve over 1 trillion US dollars annually. A state of unrestrained political corruption is known as a kleptocracy, literally meaning "rule by thieves."

Some forms of corruption -- now called "institutional corruption" -- are distinguished from bribery and other kinds of obvious personal gain. Campaign contributions are the prime example. Even when they are legal, and do not constitute a quid pro quo, they have a tendency to bias the process in favor of special interests and undermine public confidence in the political institution. They corrupt the institution without individual members being corrupt themselves. A similar problem of corruption arises in any institution that depends on financial support from people who have interests that may conflict with the primary purpose of the institution.