Twentieth century science has seen an increasingly rapid development of the differentiation of science at large by building new disciplines and specialized or interdisciplinary sub-disciplines; this has been labeled fractalization and chaos of disciplines (Abbott 2001). This increasing fragmentation of the body of sciences, with different types of qualitative and quantitative methods, forms, and norms of validation such as deductive and inductive reasoning, probabilistic and deterministic models, or even different forms of reasoning (for instance, in mathematics certain schools do not consider an indirect proof as valid or acceptable; Gonzalez 1991) call for integrating meta-levels from an inner-science perspective (Godel 1931). The construction of proper meta-levels of reflection, validation, and integration may play an important role in the future development of sciences. Science has long subscribed to a Humboldtian or Newtonian world view that has been strongly shaped by a physical rationale and was lacking an integrating, coherent system of knowledge for the investigation of human– environment interactions. Understanding of the unity of nature was perceived as the ultimate reference (von Weizsacker 1980/1971; Wilson 1999). Consilience and consistency of reasoning (Bunge 1967a, b) and a strong belief in rationality (Carnap 1991; Oppenheim and Putnam 1958) were dominant. In addition, attempts at the integration of knowledge, such as the search for a general system theory (von Bertalanffy 1951), were shaped by the thinking of natural science for a long time. The search for a unifying level or entity, or a framing of the meta-level (Godel 1931) or total transdisciplinarity, can be considered Mode 1 transdisciplinarity (Piaget 1972), which sometimes leads to the assumption of spirituality and the idea of transcendence (Nicolescu 2014). However, the challenge of integration and consistency and dealing with a complexity of systems and integrated reasoning can also be approached from a realist stance (Bunge 2003; Klein 2003; Mitchell 2003; Scholz 2011). Today, the scientific challenge has become even more complex. In the age of the Anthropocene (Crutzen 2002), instead of a ‘‘unity of nature’’ we are looking at the ‘‘resilience of inextricably coupled human–environment systems’’ (Scholz 2011) and their ontology, dynamics, and governance as a basis of sustainability science (Kates 2012). This is precisely where transdisciplinarity of the Mode 2 type (Scholz and Steiner 2015a; Gibbons et al. 1994) and the turn From a science for society to a science with society (Scholz and Stauffacher 2009; Seidl et al. 2013) serve to overcome the reductionist view of science. Transdisciplinarity requires theory and practice. Much has been written about how transdisciplinarity is conceived. However, as we discovered over the course of preparing this special feature, very few scientific papers in peer-reviewed journals document the social and scientific outcomes and benefits of transdisciplinary processes. When & Roland W. Scholz roland.scholz@igb-extern.fraunhofer.de