Sir Adrian Cedric Boult, CH (; 8 April 1889 – 22 February 1983) was an English conductor. Brought up in a prosperous mercantile family, he followed musical studies in England and at Leipzig, Germany, with early conducting work in London for the Royal Opera House and Sergei Diaghilev's ballet company. His first prominent post was conductor of the City of Birmingham Orchestra in 1924. When the British Broadcasting Corporation appointed him director of music in 1930, he established the BBC Symphony Orchestra and became its chief conductor. The orchestra set standards of excellence that were rivalled in Britain only by the London Philharmonic Orchestra (LPO), founded two years later.

Forced to leave the BBC in 1950 on reaching retirement age, Boult took on the chief conductorship of the LPO. The orchestra had declined from its peak of the 1930s, but under his guidance its fortunes were revived. He retired as its chief conductor in 1957, and later accepted the post of president. Although in the latter part of his career he worked with other orchestras, including the London Symphony Orchestra, the Philharmonia Orchestra, the Royal Philharmonic Orchestra, and his former orchestra, the BBC Symphony, it was the LPO with which he was primarily associated, conducting it in concerts and recordings until 1978, in what was widely called his "Indian summer".

Boult was known for his championing of British music. He gave the first performance of his friend Gustav Holst's The Planets, and introduced new works by, among others, Elgar, Bliss, Britten, Delius, Rootham, Tippett, Vaughan Williams and Walton. In his BBC years, he introduced works by foreign composers, including Bartók, Berg, Stravinsky, Schoenberg and Webern. A modest man who disliked the limelight, Boult felt as comfortable in the recording studio as on the concert platform, making recordings throughout his career. From the mid-1960s until his retirement after his last sessions in 1978 he recorded extensively for EMI. As well as a series of recordings that have remained in the catalogue for three or four decades, Boult's legacy includes his influence on prominent conductors of later generations, including Sir Colin Davis and Vernon Handley.