The goal of my research is to understand the fundamental limits of beam brightness in electron sources, electron guns and accelerators. I approach this goal from various angles: they range from photoemission studies via beam dynamics investigations to experiments with electron accelerators. Current projects: Development of a high brightness, high average current superconducting radio-frequency photoelectron injector (SRF photoinjector) for applications requiring continuous wave operation of a source of extremly bright electron pulses. Possible applications are energy-recovery linacs (ERL), free electron laser (FEL) or other direct beam or secondary radiation source. For the research on the SRF photoinjector my team is working on the photoemission source of electrons, the photocathode and the photocathode drive laser, as well as on the beam dynamics of space-charge dominated beams. We complement the activities with the development of beam instrumentation tools to understand and optimize the performance of such sources. Investigations into the deployment of SRF photoinjectors for ultra-fast sciences. For example for ultra-fast electron diffraction or ultra-fast electron microscopy. Development of non-destructive beam size monitors for ERL and laser-plasma accelerators.