Throughout history, seminal inventions such as the use of electricity or travelling by plane have strongly altered mankind?s way of living and working. In the last decades, a dramatic change in the workplace has been ignited by a continuously ongoing computerization and automation process. This process has been associated with reduced labor input of routine tasks and increased labor input of non-routine tasks necessitating a deep understanding of these non-routine skills and how individuals engage into them. As a result, literally all skills needed for a successful career in the 21st century seem to involve non-routine analytical and interactive cognitive skills such as general problem solving or collaboration when working in a team.To allocate people according to their individual skill level, to foster their abilities, and to systematically train them is one of society?s most crucial and essential tasks. To do so, these skills have to be understood, quantified and adequate assessment devices are needed. However, psychological research and assessment of abilities have not kept pace with the swift emerging of new and considerably more complex skills and the accompanying challenges. Thus, appropriate theoretical frameworks and measures of these non-routine skills are currently not available. This is surprising as computer-based assessment allows not only to optimize existing paper-and-pencil tests, but also provides the means necessary to specifically target the problem solving and interactive skills needed for a successful participation in today?s society.To close the gaps towards a valid understanding and assessment of 21st century skills our approach is therefore aimed towards three axes differentiated in their focus of inquiry: theoretical models, assessment instruments, and empirical application.In our first axis of work, we will seek to establish the theoretical groundwork for a profound understanding of 21st century skills and their assessment. In this first axis we will provide a state of the art understanding of Complex, Collaborative and Domain Specific Problem Solving (CPS, ColPS and DSPS) as transversal skills as well as connections to overarching theories of cognition. We will then try to elaborate an integrated theory of these 21st century skills based on an interdisciplinary approach integrating results from neuroimaging and cognitive modeling.The second research axis will guarantee that high quality and ready-to-use assessment instruments for the targeted 21st century skills, which are currently not available, will be developed. We will elaborate a generic software framework and authoring tool for the assessment of CPS, ColPS, and DSPS within one coherent open-source platform. New scoring procedures, which use the possibilities offered by log-file data, will be created and will allow a more fine-grained identification of cognitive processes used in the context of 21st century skills. Finally we will establish several pre-set versions for assessment, providing theoretically sound and psychometrically scalable instruments of high usability for all of the 21st century skills identified above and specifically targeted at different populations of respondents.The third research axis will set these newly developed instruments into action through dedicated empirical research and applications. Validation studies will be done in an initial training context and in a professional context. These validation studies will be deployed with regard to internal validity, construct validity, and ? from a mainly practical perspective ? predictive and incremental validity elaborating on the empirical real-life relevance of the targeted 21st century skills.Finally and as an outlook on the continuation and broadening of our research program, we will develop first intervention studies based on the empirical findings produced by the project.