Solution spaces for decision-making—a sustainability assessment tool for city-regions Arnim Wiek * , Claudia Binder 1 Institute for Human-Environment Systems, Department of Environmental Sciences, Swiss Federal Institute of Technology, ETH Zentrum HAD, 8092 Zurich, Switzerland Received 1 April 2004; received in revised form 1 August 2004; accepted 23 September 2004 Available online 24 March 2005 Abstract The sound development of city-regions presents a major planning challenge, as these regions are and will be the living spaces for the majority of the population. Therefore, a key question is how city- regions can be managed so that they develop in a sustainable way. Although Environmental Impact Assessment, Integrated Assessment, and other currently used approaches provide significant inputs for managing transition-processes towards sustainability, they must be extended to respond to three major deficiencies, which are (i) using lists of isolated indicators, (ii) not performing a consistency analysis of the targets to be achieved, and (iii) not utilizing the potential of transdisciplinary approaches. The authors present an approach to constructing Sustainability Solution Spaces for Decision-Making (SSP). This approach fulfils the systemic, normative, and procedural requirements of an appropriate sustainability assessment as elaborated in the technical literature. It provides a consistent set of targets considering the systemic relations among the indicators representing the city- region. This gives the decision-makers a concise guideline for sustainable decisions and makes them aware of the synergistic and contradictory effects of their decisions. The modular tool is first depicted as a general procedure and later differentiated into two transdisciplinary approaches, a participatory and an expert approach. D 2004 Elsevier Inc. All rights reserved. Keywords: Sustainability assessment; Sustainability indicators; City-regions; Decision support tool; Target conflicts; Transdisciplinarity 0195-9255/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.eiar.2004.09.009 * Corresponding author. Tel.: +41 1 632 52 60; fax: +41 1 632 10 29. E-mail address: arnim.wiek@env.ethz.ch (A. Wiek). 1 Senior authorship is not assigned. Environmental Impact Assessment Review 25 (2005) 589 – 608 www.elsevier.com/locate/eiar