The government of the U.S. State of Oklahoma, established by the Oklahoma Constitution, is a republican democracy modeled after the federal government of the United States. The state government has three branches: the executive, legislative, and judicial. Through a system of separation of powers or "checks and balances," each of these branches has some authority to act on its own, some authority to regulate the other two branches, and has some of its own authority, in turn, regulated by the other branches. The state government is based in Oklahoma City and the head of the executive branch is the Governor of Oklahoma. The legislative branch is called the Legislature and consists of the Oklahoma Senate and the Oklahoma House of Representatives. The Oklahoma Supreme Court and the Oklahoma Court of Criminal Appeals are the state's highest courts. General principles The state government of Oklahoma is divided into an executive, a legislative and a judicial branch. The governor, the state's chief executive, has a degree of direct executive power but must share executive power with other statewide elected officers. The lieutenant governor serves as the first-in-line successor to the governorship should a vacancy occur. The state legislature comprises the Oklahoma House of Representatives and the Oklahoma Senate. It passes statutes, votes on the budget, and controls the action of the executive through oversight and the power of impeachment. The President pro tempore of the Senate presides over the state senate and the Speaker of the House presides over the Oklahoma House of Representatives. Both officers are in line to succeed to the governorship in the event of a vacancy, behind the lieutenant governor. The independent judiciary is based on the common law system which evolved from use in the British Empire. It is divided into the two courts of last resort, one (the Supreme Court) dealing with civil law and the other (the Court of Criminal Appeals) dealing with criminal law. The Court on the Judiciary is responsible for monitoring the activities of judges, except those of the Supreme Court. The Court of Impeachment monitors the activities of all statewide elected officials, including the justices of the Supreme Court. Constitution A popular referendum approved the constitution of the Oklahoma on September 17, 1907, which came into effect upon Oklahoma's ratification of the United States Constitution on November 16, 1907. The ratification of both documents marked Oklahoma as the 46th US State.