The KU Leuven Junior Researcher Mobility (JuMo) concept starts from the principle that international or intersectorial mobility is an essential part of the training of young researchers to broaden their skills and career opportunities both inside and outside academia. Young researchers grow towards more independence and research excellence through the confrontation with other cultures, ideas, scientific disciplines, technologies, or other sectors like industry. Moreover, they develop their own international and intersectoral network that will prove to be useful in later career stages. JuMo will be set up by KU Leuven as part of its internal research policy plan, supported by the Flemish programme to train and improve the career prospects of PhD students and young postdoctoral researchers. It will be complementary to existing mobility programmes. The COFUND support for JuMo will allow KU Leuven to establish a postdoctoral program for outgoing mobility, with ambitions transcending the goals of the current PhD and postdoc training and career development packages at KU Leuven. Researchers at KU Leuven will be encouraged to apply for a JuMo grant for outgoing mobility for a stay of 6 to 12 months outside Belgium in a high-quality environment. This can be a renowned university, research institution, or R&D-intensive company, for which they can build on KU Leuven’s extensive international and industrial network. The program focusses on postdocs with an employment contract or fellowship in the first 5 years post PhD, and will take specific measures to compensate gender inequalities and researchers with families. JuMo proposals will be selected by the KU Leuven Research Council supported by international peers based on a clear added value for the researcher’s future career, and on arguments towards frontline research, enabling the young postdocs to build a curriculum that will improve their career prospects.