The 1918 United States Senate elections were held throughout 1918, the midpoint of Woodrow Wilson's second term as president. This was the first election since the enactment of the Seventeenth Amendment that all 32 Class 2 Senators were subject to direct or popular election, making them the final class under the old system of being selected by state legislatures. Special elections were also held to fill vacancies.

The Seventeenth Amendment to the United States Constitution established the direct election of United States senators in each state. The amendment supersedes Article I, Section 3, Clauses 1 and 2 of the Constitution, under which senators were elected by state legislatures. It also alters the procedure for filling vacancies in the Senate, allowing for state legislatures to permit their governors to make temporary appointments until a special election can be held.