The 58th United States Congress was a meeting of the legislative branch of the United States federal government, composed of the United States Senate and the United States House of Representatives. It met in Washington, DC, from March 4, 1903, to March 4, 1905, during the third and fourth years of Theodore Roosevelt's presidency. The apportionment of seats in the House of Representatives was based on the 1900 United States census. Both chambers had a Republican majority.

The 1904–05 United States Senate elections were held on various dates in various states, coinciding with President Theodore Roosevelt's landslide election to a full term and the 1904 House of Representatives elections. As these U.S. Senate elections were prior to the ratification of the Seventeenth Amendment in 1913, senators were chosen by state legislatures. Senators were elected over a wide range of time throughout 1904 and 1905, and a seat may have been filled months late or remained vacant due to legislative deadlock. In these elections, terms were up for the senators in Class 1.