Adiemus consists of composer Karl Jenkins and his Finnish "Adiemus Singers".

The session singer Miriam Stockley performed the vocal parts on the first four albums. Additional vocals were provided by Mary Carewe on all but Dances of Time, which saw the introduction of the Finnish Adiemus Singers (who would later reappear on Vocalise). Extra vocals and the chorus effects were created by overdubbing multitracked recordings of the singers (in some cases up to forty times) and varying the speed of the tape. Stockley was described by Jenkins as central to the Adiemus project due to her range and intonation, however for reasons that remain unclear she was not re-engaged for Vocalise.

The Songs of Sanctuary orchestra consisted of a string section augmented by various ethnic percussion instruments, with occasional further additions such as bells, a recorder and a quena. Mike Ratledge, with whom Jenkins had played in Soft Machine, contributed to the first album as well. Jenkins added brass and woodwind for Cantata Mundi, and continued to add more diverse instruments such as acoustic guitar on later albums. From Songs of Sanctuary to Dances of Time, the London Philharmonic Orchestra was used; Jenkins later formed his own Adiemus Orchestra to perform on The Eternal Knot recordings, returning to the LPO for Vocalise.