  Synchrotron light sources and X-ray free-electron laser (FEL) facilities are
unique tools providing extremely brilliant X-rays that allow the observation of
matter with atomic spatial resolution. On the one hand, synchrotron light
sources consist of electron circular accelerators and produce synchrotron
radiation in bending magnets and undulators. On the other hand, X-ray FEL
facilities are based on electron linear accelerators and generate more coherent
and shorter pulses suitable for time-resolved experiments. In this contribution
we will qualitatively describe synchrotron and X-ray FEL facilities. We will
start explaining some fundamental concepts related to synchrotron and FEL
radiation. We will then describe the two kinds of machines, including the
history and current facilities, the typical layout, and some basic concepts
about the electron beam dynamics and properties.
