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.
--- HISTORY AND COMMENT
The 17th Amendment, passed in 1913 and first in effect for election year 1914, amends Article 1 Section 3 of the Constitution to provide for the direct election of Senators by the people of a state rather than their appointment by a state legislature.
A series of scandalous elections in the late 19th and early 20th century led Progressives (a name they gave themselves) to call for the election on a state-wide basis of senators. The misfortunes of unintended consequences gave us state-wide advertising campaigns and finally campaign finance reforms.
Before 1913, senators were seen (in the ideal) as representing the States to the Federal Union, and representatives were seen as representing local blocks of the people. Though the reality may well have differed, the theory was quite different from what the 17th amendment created - a local representative and a state-wide "representative at large."