The Saint Louis Symphony Orchestra (SLSO) is a major United States symphony orchestra based in St. Louis, Missouri. Founded in 1880, it is the second-oldest U.S. symphony, after the New York Philharmonic. Based in Powell Symphony Hall, it performs an annual Carnegie Hall concert and makes regular overseas tours. It records on its own label, Arch Media, and has received six Grammy Awards and fifty-six nominations. The symphony has an extensive educational program; its members give some 350 free performances a year in schools and other educational settings.

The symphony has a partnership with 25 local African-American churches called IN UNISON, whose choir, drawn from church members, performs with the symphony as well as on its own programs. Also associated with the symphony are the Saint Louis Symphony Chorus and the Saint Louis Youth Symphony.

In January 2005, the orchestra's musicians went on strike over what they called an unjust contract. Two months later, the musicians and President Randy Adams agreed to a new contract that provided better wages and health care benefits.

David Robertson is the symphony's music director. Itzhak Perlman is temporarily the music advisor.