Many excitation mechanisms of matter resonate in the terahertz (THz) regime. Recent progress in the generation of intense THz radiation enables driving these excitations far out of equilibrium, providing the tools to decouple various degrees of freedom and their impact on materials’ properties. However, these sources are significantly limited in spectral tunability and efforts are ongoing to develop instrumentation for more versatile THz generation. This workshop was organized to obtain feedback from the THz community about the value of being able to generate and probe these out-of-equilibrium states with X-rays. Based on the scientific requirements and the present technological capabilities, this workshop concluded that laser-based sources are relatively inexpensive and have enabled novel experiments on specific sample systems, whereas only accelerator-based sources provide the wide tunability together with high intensity and repetition rates beyond 100 kHz, that will enable broad application at the European XFEL to the most interesting scientific problems in the field. Therefore, the suggested strategy, concluded during this workshop, is to follow two approaches simultaneously: 1) make available laser-based THz sources at every instrument at the European XFEL, based on the available pump–probe (PP) laser, and 2) evaluate two accelerator-based THz sources—one using the electron bunches from the main accelerator of the European XFEL and the other based on a separate accelerator—and ultimately develop and implement at least one of these accelerator-based sources.