The concept of wicked problems has inspired researchers in a variety of research fields, but it has also led to various discussions on, for instance, conceptual confusion and ways to tackle such complex problems. Many contemporary problems can be characterized as wicked problems: their nature is complex and there is no one best possible way to solve them. During the last decades, many insights have been developed to define characteristics of wicked problems and ways to tackle them. At present, however, (...) we need to examine the actionable knowledge accumulated in the literature to address the challenges that wicked problems create. Given the above, this introductory paper summarizes how wicked problems have evolved, what we have already learnt about them, and what scientific insights are needed to move forward. This systematic review can provide new knowledge that can lead to the development and subsequent evaluation of the wicked problems research area. (shrink)