Ketner's deep dive into previously unmined archival material allows him to convey the nuances of Group ZERO's formation as well as its many ties to international “new tendency” artists. His impressive research adds considerably to recent exhibitions and publications on ZERO by firmly situating the work of Heinz Mack, Otto Piene, and Günther Uecker in relation to lively debates about art's social and political relevance in postwar Europe.

Gregory H. Williams, Associate Professor, History of Art & Architecture, Boston University, USA

A key development in postwar European art, the German Group ZERO – and the work of its core members Piene, Mack, and Uecker – is only recently garnering the necessary English-language attention. In Witness to Phenomenon, Joseph Ketner, a longtime champion of these artists on this side of the Atlantic, chronicles a complex web of exhibitions, performances, and multi-media installations, as well as the notable contemporary critical response, introducing new audiences to ZERO and their international network of collaborators.

Lynette Roth, Daimler Curator of the Busch-Reisinger Museum, and Head, Division of Modern and Contemporary Art, Harvard Art Museums, USA