Senators in some countries are elected by the citizens through a direct vote, while in some countries, senators are appointed by the government or other public bodies. The eligibility criteria for becoming a senator vary by country, but typically include being a certain age (usually 30 or older), being a citizen of the country, and meeting any residency requirements. In the United States, for example, a senator must be at least 30 years old, a U.S. citizen for at least nine years, and a resident of the state they represent.