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 con sortium possesses the necessary models, data, and skills to set up an environment and demonstrate its func tionality 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 be come 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 train ing to use the environment, by informing the society about its possibilities, and solving a number of practi cal 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.