Mills has recorded two CDs under the project name Undark, Strange Familiar on the Emit label in 1996, re-issued on Bella Union in 2000, and Pearl & Umbra, also on Bella Union in 1999. A third Undark album being made with his long-time partner-in-sound Mike Fearon is in process, to be released in 2014-15. Since 1990 Mills has created numerous site-specific multimedia installations in the UK and abroad, all of them with contextually anchored sound as a central carrier of meaning.
A selection of mixes of these sound works will soon be released in a limited edition series to be titled Still Moves. The series will comprise of nine CDs to be housed in five hardback, full colour books in slipcases. Fully illustrated, each book will also contain interpretative texts charting the ideas behind and the evolution of each installation. Still Moves will be released by Slow Fuse Sound in 2014.