Over the past few years, the EuroHPC Joint Undertaking (EuroHPC JU) has led the construction of eight supercomputers in Europe. The most powerful of them is the supercomputer LUMI, located in Finland. LUMI is hosted by a consortium of ten countries, including Estonia. The LUMI consortium helps improve Europe’s competitiveness and digital sovereignty and promotes global research cooperation. Supercomputers enable to quickly perform complex and data-intensive calculations that a regular computer would spend too much time on. Supercomputers are indispensable in research and development and in all fields where large-scale data analysis is encountered. An overview of the world’s most powerful supercomputers is provided by the TOP500 ranking, which is updated twice a year. The supercomputer LUMI, located in the city of Kajaani, Finland, ranks fifth in the latest TOP500 table, being also the most powerful supercomputer in Europe. LUMI’s computing power is 380 petaflops (380 quadrillion calculations per second), comparable to the power of 1.5 million laptops. If a person did one calculation every second, it would take 12 billion years to do the same job. In addition to its impressive computing performance, LUMI is one of the greenest supercomputers in the world, as it uses only carbon-free hydroelectric power. The heat released during the operation of LUMI processors is used to heat the city of Kajaani. Thanks to its environmental friendliness, LUMI has already received several awards. Researchers and companies can access LUMI computing resources through the Estonian Scientific Computing Infrastructure. To date, LUMI’s computing power has already been used by several researchers from the University of Tartu and TalTech, including language technologists, geneticists, hydrologists, and chemists. One of the most ambitious international LUMI projects is the development of a digital twin of the Earth, which will play an essential role in climate and environmental research and policy-making. Apart from scientific breakthroughs, LUMI also promotes the competitiveness of the European economy, as one-fifth of the new supercomputer’s resources are intended for use by companies.