Since its first adoption by the CERN Council in 2006, the European Strategy for Particle Physics (ESPP) has served as a guiding vision and roadmap for the field in Europe. It undergoes regular updates to reflect scientific and technological progress. The first and second updates were completed in 2013 and 2020, respectively. The third update process, known as ESPPU2026, is currently underway.
Written contributions from the scientific community were submitted last March. A community symposium in June reviews the current state of the field and explores future directions. A draft strategy will then be prepared in December by a dedicated team appointed by the CERN Council, with final adoption expected in the special CERN Council session in May 2026.
Although the strategy focuses on European efforts, it has always been developed in a global context, recognising the international nature of particle physics. For example, the 2013 update encouraged strong European participation in long-baseline neutrino experiments in the U.S. and Japan, rather than pursuing an independent European project.
In a similar spirit, the strategy has long acknowledged European involvement in the International Linear Collider (ILC), although the possibility of hosting the ILC in Europe has not been considered. Following the Japanese high-energy physics community’s 2012 initiative to host the ILC in Japan as a global project, the 2013 update of the European strategy expressed a clear intention to consider European participation, waiting for a proposal from Japan. At the time, CERN’s primary focus for the future collider project in Europe was on the High-Luminosity LHC (HL-LHC) upgrade.
The 2020 update continued to highlight potential European involvement in the ILC. By that time, the HL-LHC was already in its implementation phase, and discussions had begun on the next major collider in Europe beyond the HL-LHC. In this context, the timely realization of the ILC was seen as important.
Since then, the landscape of high-energy physics has continued to evolve. With the HL-LHC upgrade approaching completion, Europe must now identify its next flagship project. Proposals such as the Future Circular Collider (FCC) at CERN and the Circular Electron Positron Collider (CEPC) in China—both of which include physics goals similar to some of those of the ILC—are now well developed. In this context, evaluating how the ILC fits into Europe’s future strategy has become a complex issue.
In its contribution to the ESPPU2026 process, the Japanese high-energy physics community has emphasised the need to first reach a global consensus on the ILC as the next major project, to be constructed through international collaboration without a predetermined host country. In discussions held by the International Expert Panel established by the International Development Team (IDT), it was noted that a misunderstanding among potential partners has led to the evolution of the ILC without first achieving this foundational agreement. Returning to this step is ambitious and likely to require more time than the ESPPU2026 timeline allows. Nevertheless, such global coordination is becoming essential, as the scale and cost of future particle physics projects continue to exceed the capacity of any single region.
Over the past few years, the IDT has advanced engineering studies for the ILC through the ILC Technology Network (ITN) and has reevaluated the ILC’s cost based on 2024 prices. A status report summarising these developments was submitted to the ESPPU2026 process in March.
It is also worth noting the strong and continuing global interest in building a linear collider based on superconducting radio-frequency (SRF) technology as the next-generation high-energy machine. A proposal to construct such a collider at CERN has been submitted to the ESPPU2026 process. Another submission outlines a long-term vision for the physics potential of a linear collider, including future upgrades to higher energies and luminosities through the adoption of advanced acceleration technologies under development. The ILC’s extensive groundwork provides a strong foundation for this evolutionary approach.
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