Sustainability challenges are often described as wicked problems (Lönngren, 2017; Norton, 2012). The term was first introduced in 1967 in a seminar at the University of California Architecture Department in Berkeley, USA. In the seminar, design professor Horst Rittel suggested “that the term ‘wicked problem’ refer to that class of social system problems which are ill-formulated, where the information is confusing, where there are many clients and decision makers with conflicting values, and where the ramifications in the whole system are thoroughly confusing. The adjective ‘wicked’ is supposed to describe the mischievous and even evil quality of these problems, where proposed ‘solutions’ often turn out to be worse than the symptoms” (Churchman, 1967, p. B141). In 1973, Horst Rittel and Melvin Webber published a seminal paper in which they described ten characteristics that distinguish wicked problems from “tame” problems (Rittel & Webber, 1973). Since 1973, the number of research papers in which the term “wicked problems” is used has steadily increased: A search in the Scopus database (12 Jan 2019) shows that, between 1973-1993, less than ten papers were published every year; this number increased to up to 54 papers per year between 1994-2011 and up to 218 papers per year between 2012-2018. Similarly, a search on “wicked problems” in Google scholar returned 15000 entries in March 2015 (McCall & Burge, 2016) and 20900 entries in January 2018. Consistent with the increasing use of the term in the research literature in general, Norton argues that the term becomes increasingly relevant for research on environmental problems since “environmental problems become more open-ended, more complex, and situation-dependent” (2012, p. 463). The term is also used in environmental and sustainability education research (ESER), for example in two research seminars at the 2016 European Conference on Educational Research. At these seminars, the presenters argued that wicked problems “bring about major challenges” for education and raise difficult questions, such as “how to deal with unstable and contested knowledge in educational processes” (Van Poeck, McKenzie, et al., 2016; Van Poeck, Östman, et al., 2016).

Despite the increasing use of the term, the research community is divided with regard to the definition and value of the term. Some researchers argue that wicked problems is a useful concept since it “alerts educators to the limitations of any vision that narrowly directs the approach to solve it” (Jordan, Kleinsasser, & Roe, 2014, p. 420) and thus enables “people to give up the unrealistic hope for scientific solutions to tame the untamable” (Xiang, 2013, p. 2). Others argue that the term is “jargon” (Anon., 2016), is put to many different (often rhetorical) uses (Turnbull & Hoppe, 2017; Xiang, 2013), lacks a “firm conceptual base” (Turnbull & Hoppe, 2017, p. 2), and is outdated (Turnbull & Hoppe, 2017). Turnbull and Hoppe further argue that “there has been no convergence whatsoever on which problems are wicked nor what we should do about them” (2017, p. 4) and that the ontological assumptions underlying the term may “perpetuate the reductionist paradigm that it was designed to overcome”(2017, p. 25). While several thematic and critical overviews of the wicked problem literature have been published (Duckett, Feliciano, Martin-Ortega, & Munoz-Rojas, 2016; Lönngren, 2017; Turnbull & Hoppe, 2017; Xiang, 2013), we have not found any systematicreview. The aim of this contribution is therefore to provide a systematic review of the wicked problems literature and thus a basis for convergence and “cumulative growth of understanding” (Borrego, Foster, & Froyd, 2014, p. 50). A further purpose is to discuss the value of the term for theoretical and empirical work in different research fields and specifically in ESER.

In 2009, Grant and Booth developed a typology of 14 different types of research reviews. In our review, we follow their description of a “systematic search and review”, which combines a systematic search of research evidence with a critical appraisal of the included literature. We also follow Borrego et al.’s description of how to conduct systematic literature reviews in developing interdisciplinary fields (such as ESER) that rely heavily on qualitative research rather than experimental studies (Borrego et al., 2014). According to Borrego et al., “systematic reviews follow transparent, methodical, and reproducible procedures that might be grouped broadly into two arenas: (1) selecting a collection of appropriate studies that will address the review question from the vast and rapidly increasing knowledge base and (2) extracting trends, patterns, relationships, and the overall picture from the collected studies” (Borrego et al., 2014, p. 50). To identify relevant literature, we search for peer-reviewed publication in general databases for journals, conference proceedings and theses. We search for papers that mention the term “wicked problem” anywhere in the publication and/or cite Rittel and Webber’s (1973) seminal paper. We then analyse and synthesise the selected publications with regard to the following questions: 1. How is the term wicked problems defined in the literature? What are important similarities and differences between descriptions of the term? 2. What ontological and epistemological assumptions underlie descriptions of wicked problems in the literature? 3. How is the value of the term wicked problems for different research purposes described in the literature? 4. What differences and similarities can be identified with regard to how the definition, underlying philosophical assumptions, and the value of the term is described in different research fields, national/cultural contexts, and/or over time?

Based on the systematic review of the literature, we critically assess the state of empirical and theoretical research on wicked problems. We attempt to identify points of convergence and divergence in the literature. In addition to these general results, we specifically discuss how the term has been used in ESER. ESER is an interdisciplinary research field with “widely differing discourses” (Sauvé, 2005) and an “extraordinary diversity of perspectives” (Ardoin, Clark, & Kelsey, 2013): research in the field is based on a large variety of ontological and epistemological assumptions. Due to this variety, we expect that our discussion of ontological and epistemological assumptions in the wicked problems in the literature will be of particular value for ESER. We expect that the perceived value of the term differs depending on basic philosophical assumptions that underlie different strands of research in ESER. Finally, we discuss implications for future research on wicked problems in ESER and other research fields.

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