Open data and models are becoming increasingly available, but there are not yet good methods and platforms to turn those into systematic evidence-based decision support. Unicorn will produce such an enviro­­nment based on existing theoretical and practical knowledge about decision support and models. This con­sortium possesses the necessary models, data, and skills to set up an environment and demonstrate its func­tionality and usefulness with several case studies related to the environmental issues, human health, and economy. The Unicorn environment will be built in a generic and systematic way so that it could even be­come an international standard for evidence-based decision support. Developing a technical environment or standard is not enough. Using the Unicorn environment is a large cul­­tural change for both researchers and decision makers, as the current decision support practices do not re­flect the principles of openness, criticism, or reuse. Therefore, this cultural change must be promoted by train­ing to use the environment, by informing the society about its possibilities, and solving a number of practi­cal and technical problems related to current practices in research institutes, ministries, and municipalities. We acknowledge these problems and offer solutions to them with an extensive interaction plan.