The International Linear Collider (ILC) Global Design Effort (GDE) has released a major milestone report, The International Linear Collider: A Technical Progress Report. As its title suggests, the 162-page report represents the current status of the global R&D that is currently co-ordinated by the GDE. Coming roughly half way through the ILC Technical Design Phase, it documents the considerable progress that has been made worldwide towards a robust and technically mature design of a 500–1000 GeV electron–positron linear collider. With a stated five-year programme for the technical design phase, the GDE felt it necessary to have a significant mid-term publication milestone that would bridge the gap between the publication of the Reference Design Report (RDR) in 2007 and that of the foreseen Technical Design Report (TDR) in 2012. Because much of the R&D referred to in the report is still ongoing, it necessarily represents a snapshot of the current situation.

The focus of the progress report is on the co-ordinated worldwide "risk-mitigating" R&D that was originally identified at the time of the RDR publication. Although the report is comprehensive in covering nearly all areas of R&D, it has a strong focus on the development of the 1.3 GHz superconducting RF accelerating technology – the heart of the linear collider design. A large fraction of the total resource available has been used to develop the necessary worldwide infrastructure and expert-base in this technology, which includes research into high-gradient superconducting cavities as well as a focus on industrialization and mass-production models for this state-of-the-art technology. A further focus is on the three beam-test facilities: TTF/FLASH at DESY Hamburg, for the superconducting RF linac; the CesrTA facility at Cornell, for damping-ring electron cloud R&D; and ATF/ATF2 at KEK, for final focus optics, instrumentation and beam stabilization. Finally, the report also indicates work towards the ILC TDR baseline design and, in particular, the conventional facilities and siting activities.

The technical progress report will serve as a solid base for the production of the final report on the technical design phase R&D, which will be part of the TDR. Some 350 authors from more than 40 institutes around the globe have contributed to its successful publication. Now attention is already turning to producing the TDR – work that will formally start at the joint ILC-CLIC workshop being held in Granada in September.

• The report, which is available online at www.linearcollider.org/interim-report, is the first of two volumes; a second volume, to be released soon by the ILC Research Directorate, will focus on the ILC scientific case and on the design of the detectors associated with the collider.