The Symphony No. 1 in B♭ minor is one of two symphonies by the English composer William Walton. The composer had difficulty in completing the work, and its first public performance was given without the finale, in 1934. The complete four-movement work was premiered the following year.
The work shows the influence of Sibelius, particularly in its musical structure. It is among the best-known symphonies by British composers, and has received numerous recordings from within a month of the 1935 premiere to the 21st century.