Neutrinos are the elementary particles that pose the most questions for us. After the neutrino oscillation experiments showed that neutrinos do have a mass, albeit a very small one, and that they mix with each other, this gives rise to many other questions. These are not only very important for the role of neutrinos in particle physics, but also for our understanding of the universe. Neutrino properties could be a major reason why the universe is made of matter while no antimatter is found. The talk will first give a brief overview of the current questions about neutrinos and the current and planned experiments to answer these questions. After that, the talk will focus on the determination of the neutrino mass. The KATRIN experiment has now recently achieved sub-eV sensitivity in direct neutrino mass measurements. The status of the experiment and an outlook will be given.