From the Guardian:-

Turner prize 2013 shortlist: Tino Sehgal dances to the fore

The deviser of unsettling public encounters is a world-class artist in a way that the other contenders – Laure Prouvost, David Shrigley and Lynette Yiadom-Boakye – are not

Tino Sehgal

And from Wikipedia

What all of Sehgal’s works have in common is that they reside only in the space and time they occupy, and in the memory of the work and its reception. The artist himself describes his works as ‘constructed situations’, whose materials are the human voice, language, movement, and interaction, without the production of physical objects.[5] His pieces are choreographies that are regularly staged in museums or galleries, and continuously executed by trained individual — Sehgal refers to them as “interpreters”[4] — for the entire duration of a show. The reaction or even participation of the spectator gives the possibility for the work to actually happen. The artwork is the constructed situation which arises between the audience and the interpreters of the piece.[6] Afterwards, the work of art will exist only in the world of experience and memory of those who directly experienced it. Sehgal’s work can be neither photographed nor illustrated; no documentation or reproduction is allowed, in order to focus all the attention on the physical evidence. For his choreographies, Sehgal regularly auditions men and women of all ages, including actors, dancers, professional singers, and ordinary people with different backgrounds. The people who are selected to interpret his work are then camouflaged among the guards and the visitors