The 17th Amendment modified Article I, Section 3, of the U.S. Constitution, by providing for the direct election of U.S. Senators by popular vote and changing the way Senate vacancies are filled. Prior to passage of the Amendment, Senators were chosen by state legislatures.
The effort to reform the election of Senators began in the 1820s, almost a century before the 17th Amendment was passed. Momentum to change the system increased around the time of the Civil War, when party divisions and political posturing led to increasing dissent in state legislatures and consequent Senate vacancies that lasted for months or sometimes years. To secure a more functional system, Congress finally passed the 17th Amendment on May 13, 1912. It was ratified by the states as of April 8, 1913.
The Senate of the United States shall be composed of two Senators from each state, elected by the people thereof, for six years; and each Senator shall have one vote. The electors in each state shall have the qualifications requisite for electors of the most numerous branch of the state legislatures.
When vacancies happen in the representation of any state in the Senate, the executive authority of such state shall issue writs of election to fill such vacancies: Provided, that the legislature of any state may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.
This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.