Fantasia on a Theme by Thomas Tallis, also known as the Tallis Fantasia, is a work for string orchestra by the British composer Ralph Vaughan Williams. It was composed in 1910 and performed for the first time on 10 September that year at Gloucester Cathedral for the Three Choirs Festival. Vaughan Williams himself conducted and the composition proved to be a major success. He revised the work twice, in 1913 and 1919. Performances generally run between 14 and 16 minutes.
The work takes its name from the original composer of the melody, Thomas Tallis (c. 1505 – 1585). Many of Vaughan Williams’ works are associated with or inspired by the music of the English Renaissance. In 1906 Vaughan Williams included Tallis’s Third Mode Melody in the English Hymnal, which he was then editing, as the melody for Joseph Addison‘s hymn When Rising from the Bed of Death. The tune is in Double Common Meter (D.C.M. or C.M.D.).