The 2021 International Workshop on Future Linear Colliders (LCWS2021), arranged by Europe, was the latest in the series devoted to the study of the physics, detectors, and accelerator issues relating to the high-energy linear electron-positron colliders CLIC and ILC. It took place in an online format.
Since the last workshop (LCWS2019), many significant steps had been made. The European Strategy for Particle Physics Update 2020 positions an electron-positron Higgs factory as the highest-priority next-generation collider. A linear collider will operate as a Higgs factory during its initial stage, while maintaining a clear path for future energy upgrades. Preparations for the ILC in Japan had moved forward with ICFA announcing the establishment of the ILC International Development Team (IDT). In the US, the Snowmass process is on-going.
With a wide programme of plenary and parallel sessions, the workshop provided the opportunity to present ongoing work as well as to get informed and involved. The programme featured progress on ILC in Japan as a prominent theme, and used the ILC-IDT working groups' substructure for sessions to review the progress in accelerator design, detector developments, and physics studies. The progress of the CLIC studies in the same areas were also covered, and most sessions and topics were common.