The polar regions play a key role in the Earth’s system. They are essential for our climate and are sentinels of climate change, human expansion, and the hunt of new resources. The polar regions are losing ice, and their oceans and land are changing rapidly. The consequences of this polar transition extend to the whole planet and are affecting people in multiple ways. Evidence-based policy recommendations are needed, but the polar regions are difficult to reach, and research infrastructures able to operate in these regions are scarce. To understand and predict key processes in the polar regions and provide evidence-based information, the polar research community needs access to world-class research infrastructure operating in these regions. POLARIN is an international network of polar research infrastructures and their services, aiming at addressing the scientific challenges of the polar regions. The network includes a wide array of complementary and interdisciplinary top level research infrastructures: Arctic and Antarctic research stations, research vessels and icebreakers operating at both poles, observatories, data infrastructures and ice and sediment core repositories. POLARIN will provide integrated, challenge-driven, and combined access to these infrastructures to facilitate interdisciplinary research on complex processes. POLARIN will: 1. Provide challenge-driven transnational access to a large portfolio of research infrastructures. 2. Improve the access to data by improving data availability and interoperability between data infrastructures. 3. Provide virtual access to data and data services. 4. Provide data products for the scientific community and decision makers. 5. Train the young generation of polar researchers in optimally exploiting the infrastructures for their research. 6. Duly advertise the services offered by POLARIN and engage the infrastructure users to share their research outcomes with society.