VOPA is an extensive collection of interactive hand signals developed by Jim Daus Hjernøe. VOPA is used to communicate non-verbally between conductor and singers to create improvisational vocal art. The system offers an advanced set of tools to lend shape and structure to the music of the moment. Both conductor and singers are able to implement live arranging, live composing, re-arranging, re-composing, use of contrasting elements such as shifting keys, modules and time signature etc. during a performance. It can also be used within traditional repertoire to convey details during rehearsals and live in concert.