The construction of the European XFEL involved many skilled trades working in parallel. A great deal of intensive work was involved in building and commissioning the most powerful X-ray laser in the world.

The story of the European XFEL's construction is one of dedication and collaboration between many different kinds of craftspeople. The construction was a cooperation between European XFEL, DESY, and many international partners.

Civil construction

The construction of the European XFEL began in 2009. As a facility that was largely underground, much of the early work involved constructing the shaft complexes that would eventually provide access to the laser's infrastructure, including the experiment hall. Over the course of nearly two years, crews dug tunnels between these complexes. In total, 5.8 km of tunnels were dug by two different machines, TULA and AMELI. TULA (standing for "Tunnel for Laser") was approximately 5 m wide and drilled the tunnels for the facility's accelerator and hard X-ray undulators. The remaining sections of the tunnel system were drilled using the 4 m wide AMELI (standing for "Am Ende Licht", German for "At the end, light").

After the completion of the tunnels, a great deal of work went into completing other underground structures, such as the experiment hall in Schenefeld. Once these areas were built and enclosed, work on the above-ground access buildings could start.

Planning, production, and installation of scientific components

Planning for the technical aspects of the facility started in 2006, with publication of the European XFEL Technical Design Report. In the ensuing years, a rigourous engineering and design phase took place, with specific components being researched and manufactured at laboratories across Europe and at the European XFEL's offices and laboratories in and around the DESY campus in Hamburg. The partner countries made special in-kind contributions, wherein specific components were developed and manufactured in national laboratories and universities inside each country. In total, 22 institutes made 79 different contributions to the facility—at a value of nearly half of the European XFEL's overall construction and commissioning costs. These contributions stimulated private industry in each of the partner countries and presented opportunities for their national institutes to develop new cutting edge techniques and technology.

One of the prime focuses of this international effort was the construction of the superconducting linear accelerator, involving 17 of the 22 contributing institutes in 8 countries. Led by DESY, the European XFEL Accelerator Consortium ensured the delivery, rigourous testing, and careful assembly of all parts of the world's longest superconducting linear accelerator. Also vital was the manufacturing, assembly, and tuning of 92 segments of the X-ray generating undulators.

As part of the construction phase, European XFEL initated an intensive research and development programme. Highly skilled scientists, engineers, and technicians established lab spaces in several buildings in and around DESY, including in the former detector hall HERA-South. There, they could work to develop and construct components, many of which were tested at synchrotron and free-electron laser facilities around the world. Among these were devices for the six specialized instruments, components for reliably providing samples within the scientific instruments, optical elements for filtering and focusing the X-ray flashes, diagnostics for monitoring the properties of the X-rays, detectors that would operate at unprecedented efficiency, and computing infrastructure for handling the data and operating the laser. Upon the completion of underground construction in 2013, the scientific and technical groups could begin installing infrastructure. The first instrument hutch structures were installed in 2014, with the heavy concrete experiment hutch for the HED instrument. Soon afterwards, the other instrument hutches began to take shape, and the tunnels were filled with beamlines, with diagnostics and X-ray optics components integrated into the beam pipes.

As for the instruments themselves, six core research and development groups formed, each tasked with the goal of assembling a state-of-the-art experiment station. The design efforts for the FXE, HED, MID, SCS, SPB/SFX, and SQS instruments pushed the envelope on developing tools for investigating biological structures, ultrafast processes, extreme states of matter, novel materials, and much more.

Finally, in 2016, the first two instruments, FXE and SPB/SFX, began taking shape, the first undulator was installed, and the linear accelerator was finished. In May 2017, the facility could produce its first X-ray laser flashes, and a month later, the X-rays could be directed into the instrument hutches for commissioning. On 1 July 2017, the facility was declared operational.