Paul Douglas Hillier (born 9 February 1949) is a conductor, music director and baritone. He specializes in early music and contemporary art music, especially that by composers Steve Reich and Arvo Pärt. He studied at the Guildhall School of Music, beginning his professional career while a vicar-scholar at St Paul's Cathedral, London. His concert debut was in 1974 in London's Purcell Room.
Born in Dorchester, England in 1949, Hillier co-founded the Hilliard Ensemble along with fellow vicar-scholar Paul Elliott and counter-tenor David James. Hillier remained the director of the ensemble until 1990, when he founded Theatre of Voices. In addition to early music, this group explores more contemporary repertoire. With the Chicago-based His Majestie's Clerkes Hillier recorded early American repertoire such as the works of William Billings on the 1992 album A Land of Pure Delight.
Hillier later became Director of the Early Music Institute at the Indiana University Jacobs School of Music and, at the same time, of the Pro Arte Singers, remaining so until he left the Institute in 2003. The Pro Arte Singers joined the Theatre of Voices in a couple of recordings. In 2001, he became the Artistic Director and Principal Conductor of the Estonian Philharmonic Chamber Choir.
- The Catch Book (2005), Oxford University Press, ISBN 0-19-343649-3, a collection of catches (comic rounds) edited by Hillier.
- A Josquin Anthology (2005), Oxford University Press, ISBN 0-19-353218-2, a collection of choral pieces by Renaissance composer Josquin des Prez, edited by Ross Duffin and Hillier.
- Writing on Music, 1965–2000 (2002), Oxford University Press, ISBN 0-19-511171-0, a collection of writings by composer Steve Reich, edited by Hillier.
- Arvo Pärt (1997), Oxford University Press, ISBN 0-19-816616-8, The first English-language biography of Estonian composer Arvo Pärt.
- English Romantic Partsongs (1986), Oxford University Press, ISBN 0-19-343650-7, a collection of songs edited by Hillier.
- 300 Years of English Partsongs: Glees, Rounds, Catches, Partsongs 1600-1900 (1983), Faber & Faber, ISBN 0-571-10045-7, a collection of music edited by Hillier.