Training young researchers to become highly-skilled leaders in developmental science is one of the major aims in SAPIENS. Our philosophy of ESR (Early Stage Researcher) training mirrors our scientific approach. ESRs will co-develop their expertise in the context of engagement in both research and training with their mentors, increasingly developing their independence and autonomy. This will prepare the ESRs for future work in diverse institutional environments (academia, SMEs, public service, NGOs) along a variety of career paths including basic research, clinical translation, applied technology, and public policy. Training in SAPIENS is provided on a local and network-wide level. On a local level, ESRs will benefit from individual supervision and local graduate training, focused on basic research skills and strengthened by cross-site supervision, where possible. Each ESR will compose a Career Development Plan, which will specify training within the three domains to the requirements of his or her research project. On a network-wide level multiple activities will be organized in which ESRs and experts collaboratively improve skills and generate new knowledge: regular training schools, monthy webinars, and secondments with SME and NGO partners to maximise the potential for effective communication and engagement of stakeholders.