During the last decades, the advent of the short-wavelength Free Electron Lasers (FELs) in the range from extreme ultraviolet (XUV) to hard X-rays has opened a new research avenue for the investigations of ultrafast electronic and structural dynamics in any form of matter. FELs deliver coherent laser pulses, combining unprecedented power densities up to \(10^{20}\) W/cm\({}^{2}\) and extremely short pulse durations down to a few femtoseconds. Thus, they offer important advantages over conventional short-wavelength light sources for many applications. Time-resolved spectroscopic and structural studies on the timescale of femtoseconds allow us to probe electrons and atoms in action. Indeed, FELs have been applied to study ultrafast charge transfer in a molecule and a molecular complex; chemical bond breaking and formation; and non-thermal phase transitions in solids. The intense, coherent and focused FEL pulses allows for the realization of single-shot diffraction imaging of non-crystallized biomolecules and nanometer-size objects. On the other hand, since the FEL pulses are entering a new regime of intensities, they are opening a new research field that involves studying the interactions between intense short wavelength laser pulses and various forms of matter. The extremely intense FEL pulse strips a certain number of electrons from an isolated atom, which leads to a violent Coulomb explosion of an isolated molecule. This instantaneously transforms a nanometer-size object into a dense nano-plasma and a single crystal into completely new disordered matter. Furthermore, rapidly developing FEL technologies allow fully coherent FEL pulses to be available routinely and permit the realization of pulse-shaping and phase-controlling of multi-color harmonic pulses. Thus, this has opened up other novel research areas of short-wavelength non-linear four-wave mixing spectroscopy and attosecond coherent control. The aim of the present special issue is to provide an overview of the recent developments of XFELs and science at XFELs as well as to predict future opportunities. For this purpose, this issue features the reports on the current status and future plans of all eight XFEL facilities in the world. Namely, [PERSON] et al. describe the FLASH (the Free Electron LASer in Hamburg) in Germany, focusing on the advanced options for FLASH2 and future perspectives [1]; [PERSON] et al. describe the recent developments and future plans of LCLS (the Linac Coherent Light Source) in the United States [2]; and [PERSON] et al. describe the status and future plans of SACLA (the Spring-8 Angstrom Compact free electron Laser) in Japan [3]. [PERSON] and [PERSON] discuss the present and future challenges at FERMI (the Free Electron laser Radiation for Multidisciplinary Investigations) in Italy, focusing on the phase-coherent multicolor pulse generations as a unique feature of FERMI [4]. Apart from these four facilities that have been in operation for the last decade, three new facilities started operations in the last couple years. This issue includes the first reports of these three facilities. [PERSON] et al. describe the construction and commissioning of PAL-XFEL (the Pohang Accelerator Laboratory X-ray Free Electron Laser) in Korea [5]; [PERSON] et al. describe the photon beam transport and scientific instruments at the European XFEL (European X-ray Free Electron Laser) [6]; and [PERSON] et al. describe SwissFEL (Swiss X-ray Free Electron Laser) [7]. In addition, [PERSON] et al. report the status of the Shanghai SXFEL (Soft X-ray Free Electron Laser) project in China [8]. The present issue also includes XFEL-pulse characterizations and instrumentations. [PERSON] et al. review the progress on ultrashort pulse characterization of XFELs [9], while [PERSON] et al. provide the measurements of the X-ray spectra of XFEL (SACLA) with a wide-range high-resolution single-shot spectrometer, which aims to measure the temporal pulse duration [10]. [PERSON] et al.