Synergy Vocals is neither a fixed choir nor an ad hoc group; rather, it consists of a pool of singers whose sound and talents can be tailored to performances of specific works. In addition to frequent appearances with major ensembles, the group has appeared on several film soundtracks. Synergy Vocals was formed in 1996 by Micaela Haslam, then a member of the Swingle Singers. The ensemble's first performance, as an all-female quartet, was of Steve Reich's Tehillim in London in 1996. Haslam remains the ensemble's director, having trained a collection of singers, female and male, in the art of close harmony singing using a microphone. In its own words, the group provides "bespoke teams of vocalists for concerts, recordings and soundtracks," with groups "whose combined sound matches the one that a composer, conductor or band has in mind for a particular piece or album." Synergy Vocals' talents are well suited to certain works the group has performed repeatedly, including Luciano Berio's Sinfonia, which Synergy Vocals has performed worldwide, and various works of Reich. The group has appeared with major orchestras and ensembles in both Europe and the U.S., including the New York Philharmonic, the Los Angeles Philharmonic, and Ensemble InterContemporain, in addition to all five BBC Orchestras. The ensemble has participated in several world premieres, including those of Reich's Three Tales and Daniel Variations, James MacMillan's Since it was the day of Preparation ..., and Louis Andriessen's La Commedia. Synergy Vocals has been heard on film and television soundtracks, including those of The Chronicles of Narnia: Voyage of the Dawn Treader, V for Vendetta, and the television series Home Fires. Synergy Vocals' recording catalog dates back to 2002, and it numbers more than 25 items. These include six solo albums of works by Reich, Berio (the Sinfonia, issued on the Harmonia Mundi label in 2016), and other composers. In 2021, Synergy Vocals was heard on a recording of John Luther Adams' Arctic Dreams on the Cold Blue Music label.