Since 2008 Susanne Mertens is working on the experimental investigation of the elusive elementary particle, the Neutrino. With the two large-scale experiments, KATRIN and LEGEND, she explores their mass and the question of whether the neutrino is its own anti-particle. Beyond that, the group of Susanne Mertens is developing a novel detector system, to search for a new type of neutrino, the so-called sterile neutrino, which could make up a large part of the dark matter of our universe.