Separation of Powers
The Framers of the Constitution feared concentration of power in any one person or governmental entity. To prevent that from occurring, the Framers created a system of checks and balances where power is divided among different branches of the government. The Constitution established three separate but equal branches of government: the legislative branch, which passes the laws; the executive branch, which administers the laws; and the judicial branch, which interprets the laws.
A table depicting the checks and balances provided under the Constitution can be found here.